U.S. patent application number 16/496567 was filed with the patent office on 2021-01-21 for engine ignition method and engine ignition device.
The applicant listed for this patent is MAHLE ELECTRIC DRIVES JAPAN CORPORATION. Invention is credited to TAKUMA AYUZAWA, MASAYUKI SUGIYAMA, NAOYA TAKAMURA.
Application Number | 20210017946 16/496567 |
Document ID | / |
Family ID | 1000005133836 |
Filed Date | 2021-01-21 |
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United States Patent
Application |
20210017946 |
Kind Code |
A1 |
AYUZAWA; TAKUMA ; et
al. |
January 21, 2021 |
ENGINE IGNITION METHOD AND ENGINE IGNITION DEVICE
Abstract
In an engine ignition method according to the present invention,
an ignition coil and an exciter coil are provided in a magneto
generator driven by an engine. After charging an ignition capacitor
using an output voltage of the exciter coil, the ignition capacitor
is discharged through a primary coil of the ignition coil at an
ignition timing of the engine, whereby a high voltage induced in a
secondary coil of the ignition coil is applied to an ignition plug
and a first spark discharge is generated in the ignition plug, and
a voltage induced in the secondary coil of the ignition coil
accompanied with rotation of the magneto rotor is applied to the
ignition plug in a state that insulation across discharge gaps of
the ignition plug is broken down due to the first spark discharge,
whereby a second spark discharge is produced in the ignition
plug.
Inventors: |
AYUZAWA; TAKUMA;
(NUMAZU-SHI, JP) ; SUGIYAMA; MASAYUKI;
(NUMAZU-SHI, JP) ; TAKAMURA; NAOYA; (NUMAZU-SHI,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MAHLE ELECTRIC DRIVES JAPAN CORPORATION |
SHIZUOKA-KEN |
|
JP |
|
|
Family ID: |
1000005133836 |
Appl. No.: |
16/496567 |
Filed: |
March 30, 2017 |
PCT Filed: |
March 30, 2017 |
PCT NO: |
PCT/JP2017/013302 |
371 Date: |
September 23, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02P 17/12 20130101;
H02J 7/345 20130101; F02P 3/0407 20130101; F02P 1/086 20130101;
H02J 7/14 20130101; F02P 2017/125 20130101; F02D 2041/0092
20130101 |
International
Class: |
F02P 1/08 20060101
F02P001/08; F02P 3/04 20060101 F02P003/04 |
Claims
1. An ignition method for producing spark discharges in an ignition
plug attached to a cylinder of an engine and performing ignition of
the engine, the method comprising the steps of: providing a magneto
generator which has a magneto rotor driven by the engine and a
stator having an armature core around which a plurality of coils
including an exciter coil, a primary coil and a secondary coil of
an ignition coil are wound as magneto coils and induces an AC
voltage in said magneto coils accompanied with rotation of the
engine, an ignition capacitor, and an ignition plug to which a
voltage induced in the secondary coil of the ignition coil is
applied; charging the ignition capacitor to one polarity with a
voltage induced in the exciter coil, then discharging, through the
primary coil of the ignition coil, electric charge accumulated in
the ignition capacitor and producing a first spark discharge across
a discharge gap of the ignition plug at an ignition timing of the
engine, and then producing a second spark discharge across the
discharge gap by applying a voltage induced in the secondary coil
of the ignition coil accompanied with a change in magnetic flux
that is inputted to the armature core from the magneto rotor, while
the discharge gap is in a state in which insulation across the
discharge gap is broken down due to the first spark discharge;
whereby the engine is ignited by the first spark discharge and the
second spark discharge.
2. The engine ignition method of claim 1, wherein, when the second
spark discharge is produced, a state is adopted in which current
flow through the exciter coil and the primary coil is
prevented.
3. An engine ignition device that applies a high voltage to an
ignition plug attached to a cylinder of an engine to produce spark
discharges in the ignition plug, the engine ignition device
comprising: a magneto generator that is provided with a magneto
rotor having a three-pole magnetic field formed at an outer
circumference of a flywheel attached to a crank shaft of the engine
and a stator having an armature core with a magnetic pole part
opposed to the poles of the magnetic field of the magneto rotor and
having plurality of coils served as magneto coils which are wound
around the armature core, the plurality of coils including an
exciter coil and a primary coil of an ignition coil and a secondary
coil of the ignition coil, the magneto generator sequentially
outputting, from the magneto coils, a first half-wave voltage, a
second half-wave voltage of a different polarity from the first
half-wave voltage, and a third half-wave voltage of the same
polarity as the first half-wave voltage during one rotation of the
crank shaft; an ignition capacitor that is provided on a primary
side of the ignition coil; a charging switch that is provided so as
to be turned on when the second half-wave voltage is induced in the
exciter coil and to form a circuit that charges the ignition
capacitor with the second half-wave voltage; an ignition switch
that is provided so as to form a discharging circuit that
discharges, through the primary coil, electric charge accumulated
in the ignition capacitor when the ignition switch is turned on; an
ignition timing detection means for generating an ignition signal
when an ignition timing of the engine is detected; and a switch
control means that is provided with a means for placing the
ignition switch to be turned on in order to produce a first spark
discharge in the ignition plug when the ignition timing is detected
and a means for controlling the ignition switch and the charging
switch so as to give rise to a state in which both the ignition
switch and the charging switch are in an open state while
insulation across a discharge gap of the ignition plug is in a
broken down state due to the first spark discharge; wherein the
engine ignition device being configured so that a second spark
discharge is produced in the ignition plug due to a voltage induced
in the secondary coil of the ignition coil accompanied with a
change in magnetic flux that is inputted to the armature core from
the magneto rotor while the insulation across the discharge gap of
the ignition plug is in the broken down state due to the first
spark discharge.
4. The engine ignition device of claim 3, wherein the engine
ignition device is provided with a rotation detection circuit that
detects a specific feature in a waveform of voltage induced in the
exciter coil and outputs a plurality of rotation detection signals
which include a rotation detection signal generated at a reference
position set at a position coming before a crank angle position
coming when a piston of the engine reaches top dead center, and a
reference signal identification means for identifying, from among
the plurality of rotation detection signals outputted by the
rotation detection circuit, a rotation detection signal generated
at the reference position as a reference signal; and the ignition
timing detection means is configured so as to detect the ignition
timing based on a timing at which the reference signal was
generated and generate an ignition signal.
5. The engine ignition device of claim 4, wherein the engine
ignition device is provided with a stroke discrimination means for
discriminating whether a stroke of the engine performed when the
reference signal was generated is a compression stroke or an
exhaust stroke; and the switch control means is configured so as to
perform control that places the ignition switch in the ON state at
the ignition timing detected by the ignition timing detection means
only when the stroke of the engine performed when the reference
signal was generated is discriminated to be a compression stroke by
the stroke discrimination means.
6. The engine ignition device of claim 5, wherein the stroke
discrimination means is provided with a breakdown voltage detection
circuit that obtains a voltage signal including information
relating to a voltage across the discharge gap of the ignition plug
from partway along the secondary coil, and is configured so as to
perform stroke discrimination on the basis of the fact that a
magnitude of the voltage signal obtained from the breakdown voltage
detection circuit when the insulation across the discharge gap of
the ignition plug is broken down differs between when a stroke of
the engine is an exhaust stroke and when a stroke of the engine is
a compression stroke.
7. The engine ignition device of claim 6, wherein a tap is led out
from a middle of the secondary coil, and the breakdown voltage
detection circuit is configured so as to detect a voltage induced
partway along the secondary coil through the tap.
8. The engine ignition device of claim 3, wherein the ignition
timing of the engine is set in a period of time during which the
second half-wave voltage induced in the exciter coil moves toward a
peak.
9. The engine ignition device of claim 3, wherein a damper diode is
connected, in parallel, across both ends of the ignition capacitor,
the damper diode being pointed in an orientation so that when the
ignition capacitor is in a state charged to one polarity, a voltage
across both ends of the ignition capacitor is applied in an
opposite direction across an anode and a cathode of the damper
diode.
10. The engine ignition device of claim 3, wherein the engine
ignition device is provided with a power supply circuit that
generates a control DC voltage using the first half-wave voltage
and the third half-wave voltage induced in the exciter coil; and
the engine ignition device is provided with a CPU that operates
using the control DC voltage generated by the power supply circuit
as a power supply voltage, and the switch control means and the
stroke discrimination means are configured by the CPU executing a
program that has been prepared in advance.
11. The engine ignition device of claim 3, wherein the primary coil
of the ignition coil is wound around a primary bobbin attached to
the armature core, a secondary bobbin is disposed so as to
encompass the primary bobbin, the secondary coil of the ignition
coil and the exciter coil are wound around the secondary bobbin,
and the secondary coil and the exciter coil are configured by
winding a single conductor around the secondary bobbin.
12. The engine ignition device of claim 3, wherein the exciter coil
is made up of a pair of coils that are wound in the same direction
and connected to one another in parallel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a capacitor discharge
engine ignition method and engine ignition device.
BACKGROUND ART
[0002] Capacitor discharge engine ignition devices, as for example
shown in Patent Document 1, are configured by an exciter coil that
is provided in a magneto generator driven by an engine and induces
an AC voltage in accompaniment with rotation of the engine, an
ignition coil that has a primary coil and a secondary coil, an
ignition capacitor that is provided on the primary side of the
ignition coil and is charged to one polarity with a voltage induced
in the exciter coil, a thyristor that is provided so as to
discharge, through the primary coil of the ignition coil, electric
charge accumulated by the ignition capacitor when an ON state is
assumed, and a control circuit that performs control so that the
thyristor is placed into the ON state at an ignition timing of the
engine (an internal combustion engine).
[0003] The magneto generator is provided with a magneto rotor that
is attached to a crank shaft of the engine, and with a stator
having an armature core and the exciter coil. The armature core has
a magnetic pole part that opposes a magnetic pole of the magneto
rotor, and the exciter coil is wound around the armature core. The
magneto generator induces an AC voltage in the exciter coil in
accompaniment with rotation of the engine. In the ignition device
shown in Patent Document 1, the ignition coil is also wound around
the armature core around which the exciter coil is wound, and the
ignition capacitor is also charged by a voltage induced in the
primary coil of the ignition coil accompanying rotation of the
magneto rotor.
[0004] In this type of ignition device, the ignition capacitor is
charged at a timing preceding an ignition timing of the engine, and
the thyristor is placed into the ON state at the ignition timing.
When the thyristor is placed into the ON state, a high-frequency
oscillating current flows on the primary side of the ignition coil
as a result of electric charge that had been accumulated by the
ignition capacitor being discharged through the thyristor and the
primary coil of the ignition coil. This primary current causes
magnetic flux having an oscillating waveform that changes at a high
frequency to flow to an iron core in the ignition coil. Change in
this magnetic flux induces a high voltage having an oscillating
waveform in the secondary coil of the ignition coil, and this high
voltage is applied to a discharge gap of an ignition plug. This
causes dielectric breakdown to occur across the discharge gap of
the ignition plug and produces a spark discharge, as a result of
which ignition of the engine is performed.
[0005] Discharge produced when a high voltage that has been induced
in the secondary coil of the ignition coil by discharging, through
the primary coil of the ignition coil, electric charge accumulated
by the ignition capacitor is applied across the discharge gap of
the ignition plug is called capacitive discharge. Capacitive
discharge is performed using a high voltage induced in the
secondary coil of the ignition coil that rises extremely quickly.
Thus, with a capacitor discharge ignition device, ignition is able
to be reliably performed at the same time a high voltage used for
ignition is generated regardless of the breakdown voltage of the
discharge gap of the ignition plug, and ignition timings can be
stabilized even when the breakdown voltage of the discharge gap of
the ignition plug is in an unstable state, such as when at high
engine speeds. However, because the release of energy accumulated
by the ignition capacitor ends after a short amount of time, a
capacitive discharge can only be sustained for very short periods
of time. For this reason, when requests are made that a duration of
spark discharges be made longer and that ignition performance be
further improved in cases in which a capacitor discharge ignition
device is used, it has been difficult to meet such demands.
[0006] Known engine ignition devices also include inductive
(current-interrupting) ignition devices with which a high voltage
is induced in a secondary coil as a result of a sudden change in
magnetic flux occurring in an iron core of an ignition coil due to
the interruption of current that had been flowing in the primary
coil of the ignition coil, and an ignition operation is performed
by applying this high voltage is applied to an ignition plug. In an
inductive ignition device, a discharge is produced in the ignition
plug by releasing energy accumulated by the ignition coil while
current had been flowing through the primary coil of the ignition
coil. Because this release of energy accumulated by the ignition
coil is performed comparatively slowly, the duration of spark
discharges is able to be made longer in cases in which an inductive
ignition device is used. Discharge produced in the discharge gap of
the ignition plug by an inductive ignition device is called
inductive discharge.
[0007] An advantage of using an inductive ignition device is that,
because the duration of spark discharges produced in the ignition
plug is able to be made longer, sufficient thermal energy can be
provided to fuel in a cylinder, and the fuel can be reliably
combusted. However, because a secondary voltage in the ignition
coil rises slowly in cases in which an inductive ignition device is
used, the timing at which discharge begins in the ignition plug
varies when at high engine speeds where the breakdown voltage of
the discharge gap of the ignition plug is unstable, and it is
difficult to stabilize ignition timings when at high engine
speeds.
[0008] As described above, there are advantages and disadvantages
to both capacitor discharge ignition devices and inductive ignition
devices. An ideal ignition spark, which rises quickly and is of
long duration, it not easily obtained using either ignition device.
It is in this light that an engine ignition device has been
proposed that aims to obtain characteristics obtained by capacitor
discharge ignition devices and characteristics obtained by
inductive ignition devices, as shown in Patent Document 2.
[0009] The ignition device shown in Patent Document 2 is provided
with an ignition capacitor that is charged with output from a DC
high-voltage power supply, a transistor switch that is connected,
in series, to a primary coil of an ignition coil and that switches
current flowing through the primary coil ON/OFF, a thyristor that
discharges, through the primary coil of the ignition coil and a
primary current control switch, an electric charge of the ignition
capacitor when an ON state is assumed, and a battery that provides
a voltage for causing a primary current to flow through primary
coil of the ignition coil and the primary current control switch.
In this ignition device, the DC high-voltage power supply, the
ignition capacitor, and thyristor, and the transistor switch
configure a capacitor discharge ignition circuit and the primary
coil of the ignition coil, the transistor switch, and the battery
configure an inductive ignition circuit, whereby the ignition
device aims to obtain characteristics obtained by capacitor
discharge ignition devices and characteristics obtained by
inductive ignition devices.
[0010] In the ignition device shown in Patent Document 2, at an
ignition timing of the engine, the thyristor is placed into the ON
state in a state in which there is electrical continuity through
the transistor switch, and after capacitive discharge has been
performed in the ignition plug by discharging the ignition
capacitor through the thyristor, the primary coil of the ignition
coil, and the transistor switch, the transistor switch is placed
into the OFF state, whereby current that had been flowing from the
battery through the primary coil of the ignition coil and the
transistor switch is interrupted and inductive discharge is
performed in the ignition plug.
PRIOR ART DOCUMENTS
Patent Documents
[Patent Document 1] Japanese Laid-open Patent Application No.
59-229055
[Patent Document 2] Japanese Laid-open Patent Application No.
2014-196674
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] Because spark discharges can only be produced in the
ignition plug for very short periods of time in cases in which a
conventional capacitor discharge ignition device is used, there is
a risk that, depending on the operating state of the engine, a
situation will arise in which ignition energy is insufficient and
complete combustion of fuel in the cylinder cannot be
performed.
[0012] As shown in Patent Document 2, it is conceivable to extend
the duration of spark discharges by adopting a configuration that
combines an inductive ignition circuit and a capacitor discharge
ignition circuit. However, because a battery is needed in order to
configure the inductive ignition circuit, the configuration shown
in Patent Document 2 is not applicable to cases in which the device
driven by the engine is not equipped with a battery.
[0013] In order for the engine to operate optimally, it is
necessary to control various control conditions, such as the speed
of the engine and a temperature of the engine, so that ignition of
the engine can be performed at optimum timings. Generally, a
rotational position of the crank shaft when a piston reaches top
dead center in a compression stroke of the engine is taken to be a
top dead center position of the compression stroke, a rotational
position of the crank shaft advanced a prescribed angle beyond the
top dead center position is taken to be a maximum advance position,
a rotational position of the crank shaft a prescribed angle behind
the maximum advance position is taken to be a maximum delay
position, and a crank position where ignition of the engine is
performed is set between the maximum advance position and the
maximum delay position.
[0014] In the present specification, the rotational position of the
crank shaft of the engine is referred to as a crank angle position,
and a crank angle position where an ignition operation of the
engine begins and a timing at which the ignition operation begins
are respectively referred to as an ignition position and an
ignition timing. Further, the crank angle positions when a piston
of the engine has reached top dead center at an end of a
compression stroke and at an end of an exhaust stroke of the engine
are respectively called a top dead center position of the
compression stroke and the top dead center position of the exhaust
stroke.
[0015] Control of the ignition timing of the engine at which
ignition is performed by a capacitor discharge ignition device, in
other words control of the ignition position, is performed by
controlling the timing that a switch (generally a thyristor) that
discharges the ignition capacitor is placed into an ON state.
Information relating to the crank angle position of the engine and
information relating to the speed of the engine are needed when
controlling the ignition timing. In the ignition device shown in
Patent Document 1, information relating to speed, and information
relating to the crank position of the engine are obtained based on
a timing at which a zero-crossing point or a peak point in a
waveform of voltage induced in a coil provided in the magneto
generator is detected and the period at which these points are
detected, to control the ignition timing of the engine. It is also
common to attach, to the engine, a pulse signal generator that
generates a pulse signal when the crank position of the engine
matches a set position and to obtain information relating to the
crank position and the speed of the engine from a pulse signal
generated by the pulse signal generator to control the ignition
timing.
[0016] As described above, in cases in which an ignition device is
configured so as to yield information relating to the speed of the
engine and information relating to the rotational position of the
crank shaft based on a waveform of voltage induced in a magneto
coil provided in the magneto generator or on a pulse signal
outputted by a pulse signal generator attached to the engine to
control an ignition timing, because an ignition operation is
performed in the vicinity of a top dead center position each time
the crank shaft goes through one rotation, when the engine in a
four-cycle engine, an ignition operation is performed not only at a
regular ignition position set in the vicinity of the top dead
center position of the compression stroke, but also at an ignition
position set in the vicinity of the top dead center position of the
exhaust stroke.
[0017] In cases in which the combustion of fuel by regular ignition
in an expansion stroke is complete, operation of the engine will
not be impeded even if ignition of the engine is performed in the
vicinity of the top dead center position of the exhaust stroke.
However, in cases in which there is insufficient combustion in the
expansion stroke, when an ignition operation is performed in the
vicinity of the top dead center position of the exhaust stroke, the
fuel remaining in the cylinder will combust and after-fire will
occur, and there is a risk of damage to the engine. Moreover, in
cases in which an ignition operation is performed both in the
vicinity of the top dead center position of the expansion stroke
and in the vicinity of the top dead center position of the
compression stroke, the life of the ignition plug is shortened
because the of the high frequency at which sparks are produced in
the ignition plug.
[0018] A main object of the present invention is to provide a
capacitor discharge engine ignition method and engine ignition
device with which, at ignition timings of an engine, spark
discharges that rise quickly and moreover have long discharge
durations are produced across a discharge gap of an ignition plug
and ignition energy can be increased without adding any circuit
elements for configuring an inductive ignition
[0019] Another object of the present invention is to provide a
capacitor discharge engine ignition method and engine ignition
device with which it is possible to discriminate whether a stroke
that ends with a piston of an engine reaching top dead center is an
exhaust stroke or a compression stroke and perform an ignition
operation only at a regular ignition timing of the engine set in
the vicinity of a top dead center position of the compression
stroke of the engine.
Means to Solve the Problems
[0020] The present invention is directed to a method for igniting
an engine by spark discharges produced in an ignition plug attached
to a cylinder of the engine and performing ignition of the
engine.
[0021] The ignition method according to the present invention
includes the steps of: providing a magneto generator which has a
magneto rotor driven by the engine and a stator having an armature
core around which a plurality of coils including an exciter coil, a
primary coil and a secondary coil of an ignition coil are wound as
magneto coils and induces an AC voltage in the magneto coils
accompanied with rotation of the engine, an ignition capacitor, and
an ignition plug to which a voltage induced in the secondary coil
of the ignition coil is applied; charging the ignition capacitor to
one polarity with a voltage induced in the exciter coil; then
discharging, through the primary coil of the ignition coil,
electric charge accumulated in the ignition capacitor and producing
a first spark discharge across a discharge gap of the ignition plug
at an ignition timing of the engine; and then producing a second
spark discharge across the discharge gap by applying a voltage
induced in the secondary coil of the ignition coil accompanied with
a change in magnetic flux that is inputted to the armature core
from the magneto rotor, while the discharge gap is in a state in
which insulation across the discharge gap is broken down due to the
first spark discharge; whereby the engine is ignited by the first
spark discharge and the second spark discharge.
[0022] In conventional capacitor discharge ignition devices,
because spark discharges can only be produced for extremely short
periods of time lasting until energy that had been accumulated in
the ignition capacitor has been completely discharged, there is
risk that ignition energy will be insufficient.
[0023] In the ignition method of the present invention, the
ignition coil is wound around the armature core of the magneto
generator together with the exciter coil so that a voltage is also
induced in the secondary coil of the ignition coil accompanied with
rotation of the magneto rotor, and after a first spark discharge is
produced in the ignition plug as a result of discharging the
ignition capacitor, a voltage induced in the secondary coil of the
ignition coil accompanied with a change in magnetic flux that is
inputted to the armature core from the magneto rotor is applied to
the ignition plug in a state in which insulation across the
discharge gap has been broken down due to the first spark
discharge, and a second spark discharge is produced across the
discharge gap of the ignition plug. As a result, the duration of
spark discharges is able to be extended.
[0024] With the present invention, after producing a quickly rising
first spark discharge at an ignition timing, a second spark
discharge is generated while a voltage greater than or equal to a
threshold value is being applied across the discharge gap of the
ignition plug from the secondary coil of the ignition coil. This
produces spark discharges that rise quickly and moreover have long
durations, enabling ignition timings to be stabilized and ignition
energy to be increased.
[0025] The second spark discharge is produced by applying across
the discharge gap of the ignition plug a voltage induced in the
secondary coil of the ignition coil due to a change in magnetic
flux produced in the armature core accompanied with rotation of the
magneto rotor in a state that insulation across the discharge gap
is broken down. The second spark discharge continues for a period
during which the secondary coil generates a voltage greater than or
equal to a threshold value which is a lower limit for a voltage
that needs to be applied across a discharge gap across which
insulation is broken down in order to produce a discharge across
the discharge gap. In this point, the second spark discharge
differs from the inductive discharge which is produced only until
energy that had been accumulated in the ignition coil has been
completely released when an inductive ignition device is used.
[0026] In order to carry out the ignition method of the present
invention, after generating a first spark discharge, a voltage of a
level needed in order to produce a second spark discharge across a
discharge gap of an ignition plug needs to be reliably induced in
the secondary coil of the ignition coil, while insulation across
the discharge gap is in a broken down state.
[0027] After a first spark discharge is generated, a phenomenon
(armature reaction) such that magnetic flux flowing through the
armature coils is reduced and/or changes in the magnetic flux
produced in the armature core accompanied with rotation of the
magneto rotor are counteracted, may occur due to the synthesis of
magnetic flux that is inputted to the armature core from the
magneto rotor and magnetic flux flowing to the armature core from
the magneto coils wrapped around the armature core. In order to
reliably induce a voltage for producing a second spark discharge in
the secondary coil, it is necessary to ensure, to the extent
possible, that the above phenomenon does not occur immediately
after a first spark discharge is generated. To do so, it is
preferable that current flow through at least the exciter coil and
the primary coil of the magneto coils wound around the armature
core of the magneto generator is prevented, when a second spark
discharge is produced.
[0028] The present invention is further directed to an engine
ignition device that applies a high voltage to an ignition plug
attached to a cylinder of an engine and produces spark discharges
in the ignition plug. The engine ignition device according to the
present invention is configured by: a magneto generator that is
provided with a magneto rotor having a three-pole magnetic field
formed at an outer circumference of a flywheel attached to a crank
shaft of the engine and a stator having an armature core with a
magnetic pole part opposed to the poles of the magnetic field of
the magneto rotor and having plurality of coils served as magneto
coils which are wound around the armature core, the plurality of
coils including an exciter coil and a primary coil of an ignition
coil and a secondary coil of the ignition coil, the magneto
generator sequentially outputting, from the magneto coils, a first
half-wave voltage, a second half-wave voltage of a different
polarity from the first half-wave voltage, and a third half-wave
voltage of the same polarity as the first half-wave voltage during
one rotation of the crank shaft; an ignition capacitor that is
provided on a primary side of the ignition coil; a charging switch
that is provided so as to be turned on when the second half-wave
voltage is induced in the exciter coil and to form a circuit that
charges the ignition capacitor with the second half-wave voltage;
an ignition switch that is provided so as to form a discharging
circuit that discharges, through the primary coil, electric charge
accumulated in the ignition capacitor when the ignition switch is
turned on; an ignition timing detection means for generating an
ignition signal when an ignition timing of the engine is detected;
and a switch control means that is provided with a means for
placing the ignition switch to be turned on in order to produce a
first spark discharge in the ignition plug when the ignition timing
is detected and a means for controlling the ignition switch and the
charging switch so as to give rise to a state in which both the
ignition switch and the charging switch are in an open state while
insulation across a discharge gap of the ignition plug is in a
broken down state due to the first spark discharge; wherein the
engine ignition device being configured so that a second spark
discharge is produced in the ignition plug due to a voltage induced
in the secondary coil of the ignition coil accompanied with a
change in magnetic flux that is inputted to the armature core from
the magneto rotor while the insulation across the discharge gap of
the ignition plug is in the broken down state due to the first
spark discharge.
[0029] In one preferred aspect of the present invention, the engine
ignition device is provided with a rotation detection circuit that
detects a specific feature in a waveform of voltage induced in the
exciter coil and outputs a plurality of rotation detection signals
which include a rotation detection signal generated at a reference
position set at a position coming before a crank angle position
coming when a piston of the engine reaches top dead center, and a
reference signal identification means for identifying, from among
the plurality of rotation detection signals outputted by the
rotation detection circuit, a rotation detection signal generated
at the reference position as a reference signal; and the ignition
timing detection means is configured so as to detect the ignition
timing based on a timing at which the reference signal was
generated and generate an ignition signal.
[0030] In the present specification, a "specific feature" in a
waveform of voltage induced in the exciter coil is a feature that,
of the parts of the voltage waveform, is able to be distinguished
and specified from among other portions of the voltage waveform.
This is, for example, a zero-crossing point, a peak point, a point
where an instantaneous value reaches a set threshold level, or the
like.
[0031] In another aspect of the present invention, the engine
ignition device is provided with a stroke discrimination means for
discriminating whether a stroke of the engine performed when the
reference signal was generated is a compression stroke or an
exhaust stroke. In this case, the switch control means is
configured so as to perform control that places the ignition switch
in the ON state at the ignition timing detected by the ignition
timing detection means only when the stroke of the engine performed
when the reference signal was generated is discriminated to be a
compression stroke by the stroke discrimination means.
[0032] The stroke discrimination means can be provided with a break
down voltage detection circuit that obtains a voltage signal
including information relating to a voltage across the discharge
gap of the ignition plug from partway along the secondary coil, and
can be configured so as to perform stroke discrimination on the
basis of the fact that a magnitude of a voltage signal obtained
from the breakdown voltage detection circuit when the insulation
across the discharge gap of the ignition plug is--broken down
differs between when a stroke of the engine is an exhaust stroke
and when a stroke of the engine is a compression stroke.
[0033] To detect the dielectric breakdown voltage of the ignition
plug without being influenced by high voltage induced in the
secondary coil of the ignition coil, it is preferable, for example,
that a tap be led out from a middle of the secondary coil, and that
the breakdown voltage detection circuit be configured so as to
detect a voltage induced partway along the secondary coil through
the tap.
[0034] When the stroke discrimination means is provided as above
and the switch control means is configured so as to perform control
that places the ignition switch in the ON state at the ignition
timing detected by the ignition timing detection means only when
the stroke of the engine when the reference signal was generated is
discriminated to be a compression stroke by the stroke
discrimination means, an ignition operation can be prevented from
being performed in a final stage of an exhaust stroke, enabling the
combustion of gas and the generation of after-fire to be prevented
in cases in which uncombusted gas is left in the cylinder in an
exhaust stroke as a result of fuel not being completely combusted
in a expansion stroke, such as during sudden acceleration of the
engine.
[0035] Moreover, when the stroke discrimination means is provided
as above, wasteful ignition is not performed in a final stage of an
exhaust stroke, enabling the ignition capacitor to be charged to a
sufficiently high voltage in a period leading up to an ignition
timing, and enabling a reduction in ignition performance due to an
insufficient ignition capacitor charging voltage to be
prevented.
[0036] When configured as above, wasteful ignition is not performed
in a final stage of an exhaust stroke. This prevents needless wear
on the electrodes of the ignition plug, enabling the life of the
ignition plug to be extended.
[0037] In cases in which a magneto generator provided with a
magneto rotor formed with a three-pole magnetic field at the outer
circumference of a flywheel attached to a crank shaft of the engine
is used, of the first half-wave voltage to the third half-wave
voltage, the voltage with the highest peak value is the second
half-wave voltage. Consequently, it is preferable that the ignition
timing be set in a period of time during which the second half-wave
voltage induced in the exciter coil moves toward a peak, and that
the switch control means places the ignition switch into the ON
state at such ignition timing. With this configuration, when both
the ignition switch and the charging switch have been placed into
the open state after a first spark discharge is generated in the
ignition plug, a voltage greater than or equal to a threshold value
is reliably applied to the ignition plug from the secondary coil of
the ignition coil, enabling a second spark discharge to be reliably
produced.
[0038] Further, in case in which a magneto generator such as that
described above is used, of the first half-wave voltage to the
third half-wave voltage induced in the exciter coil, the half-wave
with the greatest width is the second half-wave voltage.
Accordingly, when the ignition timing is set in an interval in
which the second half-wave voltage moves toward a peak, the amount
of time over which an output voltage of the magneto generator is
applied to the ignition plug from the secondary coil of the
ignition coil after the first spark discharge is produced is made
longer, enabling the amount of time over which a second spark
discharge is produced to be made longer, and enabling a greater
amount of ignition energy to be obtained.
[0039] In a preferred aspect of the ignition device according to
the present invention, a damper diode is connected, in parallel,
across both ends of the ignition capacitor, the damper diode being
pointed in an orientation so that when the ignition capacitor is in
a state charged to one polarity, a voltage across both ends of the
ignition capacitor is applied in an opposite direction across an
anode and a cathode of the damper diode.
[0040] When the damper diode is connected in parallel to the
ignition capacitor in such manner, an interval of an initial
half-wave of high voltage induced in the secondary coil of the
ignition coil when the ignition capacitor has been discharged can
be made longer, enabling a set-up for consecutively generating a
first spark discharge and a second spark discharge to be
simplified.
[0041] In a preferred aspect of the ignition device according to
the present invention, the engine ignition device is provided with
a power supply circuit that, using the first half-wave voltage and
the third half-wave voltage induced in the exciter coil as a power
supply voltage, generates a control DC voltage, and the engine
ignition device is provided with a CPU that operates using the
control DC voltage generated by the power supply circuit as a power
supply voltage, and the switch control means and the stroke
discrimination means are configured by the CPU executing a program
that has been prepared in advance.
[0042] With this configuration, the present invention can also be
applied to engine drive apparatuses not equipped with a
battery.
[0043] In another preferred aspect of the ignition device according
to the present invention, the primary coil of the ignition coil is
wound around a primary bobbin attached to the armature core, a
secondary bobbin is disposed so as to encompass the primary bobbin,
and the secondary coil of the ignition coil and the exciter coil
are wound around the secondary bobbin. Further, the secondary coil
and the exciter coil are configured by winding a single conductor
around the secondary bobbin.
[0044] With this configuration, winding of the ignition coil and
the exciter coil can be simplified, enabling manufacturing costs to
be reduced.
[0045] In a preferred aspect of the ignition device according to
the present invention, the exciter coil is configured by a pair of
coils that are wound in the same direction and connected to one
another in parallel.
[0046] When the exciter coil is configured in this manner, a
resistance of the exciter coil is reduced and loss in the circuit
that charges the ignition capacitor is reduced, enabling the
ignition capacitor to be charged to a higher voltage.
[0047] Other aspects of the present invention will be made more
apparent in the description of the embodiment for carrying out the
present invention given below.
Advantageous Effects of the Invention
[0048] With the present invention, after a first spark discharge is
produced in the ignition plug as a result of discharging, through
the primary coil of the ignition coil, electric charge accumulated
by the ignition capacitor at an ignition timing of the engine, a
voltage induced in the secondary coil of the ignition coil due to a
change in magnetic flux that is inputted to the armature core from
the magneto rotor is applied to the ignition plug in a state that
insulation across the discharge gap of the ignition plug is broken
down due to the first spark discharge, whereby a second spark
discharge is next produced in the ignition plug. As a result, spark
discharges are produced that rise quickly and moreover have much
longer durations than when a conventional capacitor discharge
ignition device is used, enabling ignition timings to be stabilized
and ignition energy to be increased, and enabling performance of
the engine ignition device to be improved.
[0049] Further, in the present invention, in cases in which the
engine ignition device is provided with a stroke discrimination
means for discriminating whether a stroke of the engine when a
reference signal used for detecting a reference position when an
ignition timing is detected was generated is a compression stroke
or an exhaust stroke, and the switch control means is configured so
as to perform control that places the ignition switch in the ON
state at the ignition timing detected by the ignition timing
detection means only when the stroke of the engine when the
reference signal was generated is discriminated to be a compression
stroke by the stroke discrimination means, combustion in an exhaust
stroke and the generation of after-fire can be prevented in cases
in which the combustion of fuel in a power stroke is incomplete,
such as during sudden acceleration of the engine. Because wasteful
discharge is no longer performed in the ignition plug in a final
stage of an exhaust stroke, the life of the ignition plug is able
to be prolonged. Moreover, because engine stroke discrimination is
performed on the basis of the fact that a voltage detected from the
secondary coil of the ignition coil differs between a compression
stroke and an exhaust stroke of the engine, and without using a cam
sensor or other electromechanical sensor, the ignition device is
able to be endowed with stroke discrimination functionality without
incurring increased cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a front view illustrating a hardware configuration
of an embodiment of an engine ignition device according to the
present invention in partial cross-section;
[0051] FIG. 2 is a cross-sectional view illustrating configuration
of relevant parts of the embodiment of FIG. 1;
[0052] FIG. 3 is a cross-sectional view illustrating half of a
modified example of a magneto rotor of a magneto generator that can
be used in an embodiment of the present invention;
[0053] FIG. 4 is a circuit diagram illustrating an example circuit
configuration of the ignition device of the embodiment illustrated
in FIG. 1;
[0054] FIG. 5 is a circuit diagram illustrating another example
configuration of the circuit of the ignition device of the
embodiment illustrated in FIG. 1;
[0055] FIG. 6 is a circuit diagram illustrating yet another example
configuration of the circuit of the ignition device of the
embodiment illustrated in FIG. 1;
[0056] FIG. 7 is a block diagram illustrating configuration of a
microcomputer used in the present embodiment;
[0057] FIG. 8 is a block diagram illustrating configuration of a
control unit used in the present embodiment;
[0058] FIG. 9 is a timing chart for explaining operation of the
embodiment illustrated in FIG. 4;
[0059] FIG. 10 is a flowchart illustrating an overall flow of a
program executed by the microcomputer used in the embodiment
illustrated in FIG. 1;
[0060] FIG. 11 is a flowchart illustrating an algorithm for an
initialization process executed by the microcomputer used in the
embodiment illustrated in FIG. 1;
[0061] FIG. 12 is a flowchart illustrating an algorithm for a main
process executed by the microcomputer used in the embodiment
illustrated in FIG. 1;
[0062] FIG. 13 is a flowchart illustrating an algorithm for a
rotation detection signal interrupt process executed by the
microcomputer used in the embodiment illustrated in FIG. 1;
[0063] FIG. 14 is a flowchart illustrating an algorithm for a timer
1 interrupt process executed by the microcomputer used in the
embodiment illustrated in FIG. 1;
[0064] FIG. 15 is a flowchart illustrating part of an algorithm for
a timer 0 interrupt process executed by the microcomputer used in
the embodiment illustrated in FIG. 1; and
[0065] FIG. 16 is a flowchart illustrating the rest of the
algorithm for a timer 0 interrupt process executed by the
microcomputer used in the embodiment illustrated in FIG. 1.
MODE FOR CARRYING OUT THE INVENTION
<Ignition Method According to the Present Invention>
[0066] As stated above, because a high voltage used for ignition
that rises quickly can be applied to the ignition plug in cases in
which a capacitor discharge ignition method is used, ignition is
able to be reliably performed at the same time a high voltage used
for ignition is generated regardless of the breakdown voltage of
the discharge gap of the ignition plug, and ignition timings can be
stabilized. However, the release of energy accumulated in the
ignition capacitor ends after a short amount of time, and because
spark discharges (capacitive discharges) obtained as a result of
discharging the ignition capacitor can only be sustained for very
short periods of time, in cases in which a capacitor discharge
ignition method is used, it is not possible to obtain an amount of
ignition energy as large as that due to inductive discharge.
[0067] The present inventors considered that if the ignition coil
is wound around the armature core of the magneto generator, and
after a first spark discharge is produced in the ignition plug as a
result of a high voltage induced in the secondary coil of the
ignition coil by discharging the ignition capacitor, a voltage
induced in the secondary coil of the ignition coil due to a change
in magnetic flux inputted to the armature core from the magneto
rotor is applied to the ignition plug while insulation across the
discharge gap of the ignition plug is in broken down state (a state
in which discharge can be produced by the mere application of a
comparatively low voltage across the discharge gap) due to the
first spark discharge, the first spark discharge and the second
spark discharge are consecutively generated and the duration of
spark discharge could be greatly extended.
[0068] The present invention has been made on the basis of ideas
such as described above, and an ignition method according to the
present invention includes the steps of providing a magneto
generator which has a magneto rotor driven by the engine and a
stator having an armature core around which a plurality of coils
including an exciter coil, a primary coil and a secondary coil of
an ignition coil are wound as magneto coils and induces an AC
voltage in each magneto coil accompanied with rotation of the
engine, an ignition capacitor, and an ignition plug to which a
voltage induced in the secondary coil of the ignition coil is
applied; charging the ignition capacitor to one polarity with a
voltage induced in the exciter coil; discharging, through the
primary coil of the ignition coil, electric charge accumulated by
the ignition capacitor and producing a first spark discharge across
a discharge gap of the ignition plug at an ignition timing of the
engine; and then producing a second spark discharge across the
discharge gap by applying a voltage induced in the secondary coil
of the ignition coil accompanied with a change in magnetic flux
that is inputted to the armature core from the magneto rotor, while
the discharge gap is in a state in which insulation thereacross is
broken down due to the first spark discharge; and performing
ignition of the engine using the first spark discharge and the
second spark discharge.
[0069] With the present invention, after first producing a quickly
rising capacitive discharge at an ignition timing (when ignition
begins) and then promptly producing a spark discharge in the
ignition plug, a spark discharge is able to be sustained while an
output voltage of the magneto generator is being applied across the
discharge gap of the ignition plug from the secondary coil of the
ignition coil. This produces spark discharges that rise quickly and
moreover have long durations, enabling ignition timings to be
stabilized and ignition energy to be increased.
[0070] The second spark discharge is produced by applying a voltage
induced in the secondary coil of the ignition coil accompanied with
rotation of the of the magneto rotor across the discharge gap of
the ignition plug in a state that insulation thereacross is broken
down. The second spark discharge continues for a period during
which the secondary coil generates a voltage greater than or equal
to a threshold value. In this point, the second spark discharge
differs from the inductive discharge which is produced only until
energy accumulated in the ignition coil is completely released in
cases in which an inductive ignition device is used.
[0071] After various experimentation with the ignition method
according to the present invention, it became apparent that a spark
discharge of a long duration that contributes to ignition could not
be reliably produced following a capacitive discharge by merely
adopting a configuration in which the ignition coil of a capacitor
discharge ignition device is wound around the armature core of a
magneto generator.
[0072] Upon further deliberation, it was surmised that the reason
why only capacitive discharge could be produced even after
providing the ignition coil in the magneto generator and inducing
an output voltage of the magneto generator in the secondary coil of
the ignition coil is because, due to armature reaction produced by
current flow through a magneto coil other than the secondary coil
of the ignition coil immediately after the ignition capacitor has
been discharged, a voltage greater than or equal to the threshold
value cannot be induced in the secondary coil of the ignition coil
immediately after the ignition capacitor has been discharged.
[0073] From this, it became apparent that when carrying out the
ignition method according to the present invention, in order to
ensure, to the extent possible, that armature reaction is not
produced in the magneto generator when a second spark discharge is
produced, it is preferable that, of magneto coils other than the
secondary coil of the ignition coil, there be no current flow
through at least the primary coil of the ignition coil and the
exciter coil when a second spark discharge is produced.
[0074] As described above, in order to induce a voltage greater
than or equal to a threshold value in the secondary coil of the
ignition coil when a second spark discharge is produced, it is
preferable that a state be adopted in which, of magneto coils other
than the secondary coil of the ignition coil, there is no current
flow through at least the exciter coil and the primary coil of the
ignition coil. In such case, control for ensuring that there is no
current flow through the exciter coil may be performed immediately
before producing a second spark discharge, or this control may be
performed at any timing set in an interval from a timing at which
charging of the ignition capacitor finishes and a timing at which
the second spark discharge is produced.
<Example Configuration of the Magneto Generator Used in
Embodiments of the Ignition Device According to the Present
Invention>
[0075] Next, embodiments of an ignition device that carry out an
ignition method according to the present invention will be
described.
[0076] Although the present invention can be applied to
single-cylinder engines and to multiple-cylinder engines, in the
following embodiments the engine is a single-cylinder engine in
order to facilitate explanation.
[0077] FIGS. 1 to 4 illustrate an embodiment of an engine ignition
device according to the present invention. FIG. 1 is a front view
illustrating configuration of relevant parts of a magneto generator
used in the present embodiment in partial cross-section. FIG. 2 is
an enlarged cross-sectional view illustrating relevant parts of the
magneto generator of FIG. 1. FIG. 3 is a cross-sectional view
illustrating a modified example of a rotor of a magneto generator
that can be used in an ignition device according to the present
invention. FIG. 4 is a circuit diagram illustrating a circuit
configuration of an engine ignition device according to the present
embodiment.
[0078] In FIG. 1, 1 is an outer-magnet type magneto generator that
is used in the present embodiment. The generator 1 illustrated is
configured by a magneto rotor 2 and a stator 3. The magneto rotor 2
is configured by a flywheel 201 that is attached to a crank shaft
of an engine (not illustrated), and a permanent magnet 202 that is
attached to an outer circumferential part of the flywheel 201. At
least the outer circumferential part of the flywheel 201 is
configured by a ferromagnetic material such as iron. A recess 203
is formed in the outer circumferential part of the flywheel 201,
and an arcuate permanent magnet 202 is attached inside the recess
203 by adhesion or the like. The permanent magnet 202 is magnetized
along a radial direction of the flywheel 2. A three-pole magnetic
field is configured at the outer circumferential part of the
flywheel by three magnetic poles. These three magnetic poles
include a magnetic pole (an N pole in the example illustrated) 2b
at the outer circumferential side of the permanent magnet 202 and
magnetic poles (S poles in the example illustrated) 2a and 2c drawn
out from the inner circumferential side of the permanent magnet 202
and onto outer circumferential parts of the flywheel on both sides
of the recess 203.
[0079] The stator 3 is configured by an armature core 3A and a coil
unit 3B that is wound around the armature core 3A. The armature
core 3A is a laminated body made of sheet steel, and at each end
has magnetic pole parts 3a and 3b that oppose the magnetic poles 2a
to 2c of the magnetic field. As described below, in the present
embodiment, an electronics unit 4 configuring an engine ignition
device is integrally formed to the coil unit 3B.
[0080] Described in further detail, the armature core 3A is
configured so that an I-shaped coil winding part 301 and a pair of
projecting pole units 302a, 302b coupled to both ends of the coil
winding part 301 present substantially a U-shape. The magnetic pole
parts 3a and 3b are formed at a respective tip of the projecting
pole units 302a and 302b. These magnetic pole parts are made to
oppose the magnetic poles 2a to 2c of the magnetic field of the
magneto rotor 2 across a gap.
[0081] As is also illustrated in FIG. 2, the coil unit 3B has a
structure in which a primary bobbin 303 that is provided so as to
encircle the coil winding part 301 of the armature core 3A, a
primary coil L.sub.1 of an ignition coil that is wound around the
primary bobbin 303, a secondary bobbin 304 that is attached to the
armature core in a state in which a main part of the primary bobbin
is housed to the inside thereof, a plurality of coils that are
wound around the secondary bobbin 304, and the electronics unit 4,
which is disposed at an outer side of the coils wound around the
secondary bobbin 304, are accommodated within a case 306, and in
which the coil unit 3B is molded to components housed within the
case 306 using insulating resin 309 that is filled into the case
306. First and second secondary coils L.sub.21 and L.sub.22, which
configure a secondary coil L.sub.2 of the ignition coil, and an
exciter coil Lex, are wound around the secondary bobbin 304.
[0082] The primary bobbin 303 has a coil winding body part 303a and
flange parts 303b and 303c. The flange parts 303b and 303c are
respectively provided at one end side and the other end side of the
coil winding body part 303a along an axial direction thereof. The
primary coil L.sub.1 is wound around the outer periphery of the
body part 303a.
[0083] The secondary bobbin 304 has, integrated together as a
single unit, a first coil winding body part 304a, a flange part
304b, a second coil winding body part 304c, a flange part 304d, a
third coil winding body part 304e, a flange part 304f, and a flange
part 304g. The first coil winding body part 304a is disposed so as
to encompass the primary coil L.sub.1. The flange part 304b is
formed at one axial direction end of the first coil winding body
part 304a. The second coil winding body part 304c is formed
adjacent to the other axial direction end of the first coil winding
body part 304a. The flange part 304d separates the first coil
winding body part 304a and the second coil winding body part 304c.
The third coil winding body part 304e is provided at a position
offset radially inward of the body part 304c at a position adjacent
to the second coil winding body part 304c. The flange part 304f
separates the second coil winding body part 304c and the third coil
winding body part 304e. The flange part 304g is formed to an end of
the third coil winding body part 304e on the opposite side of the
third coil winding body part 304e to the flange part 304f. The
first secondary coil L.sub.21 and the second secondary coil
L.sub.22 are wound around the first coil winding body part 304a and
the second coil winding body part 304c, respectively, and the
exciter coil Lex is wound around the third coil winding body part
304e.
[0084] In the present embodiment, a single conductor is
continuously wound to form the first and second secondary coils
L.sub.21 and L.sub.22. The second secondary coil L.sub.22 has fewer
windings than the first secondary coil L.sub.21, and as illustrated
in FIG. 4, a tap B is led out from a point where the secondary
coils are connected. An ungrounded output terminal A of the
secondary coil is led out from an end of the first secondary coil
L.sub.21 on the opposite side of the first secondary coil L.sub.21
to the tap B, and a grounded output terminal C of the secondary
coil is led out from an end of the second secondary coil L.sub.22
on the opposite side of the second secondary coil L.sub.22 to the
tap B.
[0085] Although in the example illustrated the exciter coil Lex is
wound around the secondary bobbin, the exciter coil can be wound
around the primary bobbin.
[0086] The electronics unit 4 is configured by mounting electronic
components 402 configuring electronic circuitry portion of an
engine ignition device to a circuit board 401. The electronics unit
4 is disposed in a state in which a main face (face with the
largest surface area) of the circuit board 401 points in a
direction following axes of the primary coil L.sub.1 and the
secondary coil L.sub.2. In the example illustrated, projecting
parts 304d1, 304f1, and 304g1 that project radially outward are
respectively provided to sections of outer peripheral parts of the
flange parts 304d, 304f, and 304g of the secondary bobbin 304, and
the circuit board 401 is secured to these projecting parts by
adhesion or other suitable means, whereby the circuit board 401 is
supported with respect to the secondary bobbin 304.
[0087] The case 306 has a bottomed case body 306a and a cover plate
306b. The case body 306a houses the primary coil L.sub.1 wound
around the primary bobbin 303, the secondary coil and the exciter
coil wound around the secondary bobbin 304, and the electronics
unit 4. The cover plate 306b closes off an opening in the case body
306a. A high-voltage cord retaining part 306c that retains one end
of a high-voltage cord 5 is integrally provided to an outer
peripheral part of the cover plate 306b. An output line 307 led out
from the ungrounded output terminal A (see FIG. 4) of the secondary
coil L.sub.2 of the ignition coil is connected to one end of a core
of the high-voltage cord 5 retained by the high-voltage cord
retaining part 306c. The other end of the core of the high-voltage
cord 5 is connected to an ungrounded terminal of an ignition plug
attached to the cylinder of the engine. An earth lead 308 is drawn
out from an earth terminal of the circuit board 401. This earth
lead passes through the cover plate 306b of the case and leads to
the outside. The insulating resin 309 is filled into the case 306,
and this insulating resin is molded around components housed the
case 306.
[0088] The armature core 3A is disposed in a state in which the
coil winding part 301 has been passed through an iron-core through
hole h.sub.1 provided in the cover plate 306b, the coil winding
body part 303a of the primary bobbin 303, the third coil winding
body part 304e of the secondary bobbin 304, and an iron-core
through hole h.sub.2 provided in a bottom part of the case body
306a. The armature core 3A and the coil unit 3B configure the
stator 3.
[0089] Although in the present embodiment the engine is a
single-cylinder engine, in cases in which the engine is a
multiple-cylinder engine, a stator 3 is provided to each cylinder
of the engine, and in each cylinder, an ignition operation is
performed when the magnetic pole parts 2a to 2c of the magneto
rotor 2 pass by the positions of the magnetic pole parts 3a and 3b
of the stator 3 provided to each cylinder. Each stator 3 is
disposed at a position suited to cause an ignition operation to be
performed in the corresponding cylinder, and is secured to a stator
attachment part provided to a case or the like of the engine.
[0090] In the example illustrated in FIG. 1, attachment holes 302a1
and 302b1 are respectively provided passing through the projecting
pole units 302a, 302b of the armature core. The stator 3 is
fastened to a stator attachment part by screws respectively passed
through these attachment holes. In a state in which the stator 3
has been secured to the stator attachment part, the magnetic pole
parts 3a and 3b formed at the tips of the projecting pole units
302a and 302b are made to oppose a region provided with the
magnetic poles 2a to 2c at the outer circumferential part of the
magneto rotor 2 across a gap.
[0091] In the magneto generator used in the present embodiment, due
to the exciter coil Lex and the primary coil L.sub.1 and the
secondary coil L.sub.2 of the ignition coil being wrapped around
the armature core 3A, not only is an output voltage of the magneto
generator voltage induced in the exciter coil Lex, but an output
voltage of the magneto generator is induced in the primary coil
L.sub.1 and the secondary coil L.sub.2 of the ignition coil as
well.
[0092] In the illustrated magneto generator, over the course of a
single rotation by the magneto rotor 2, changes such as that
illustrated in FIG. 9(A) arise in magnetic flux .phi. flowing
through the armature core 3A. As illustrated in FIG. 9(B), this
change in magnetic flux sequentially induces, in the exciter coil
Lex, a first half-wave voltage V.sub.1, a second half-wave voltage
V.sub.2 of an opposite polarity to that of the first half-wave
voltage V.sub.1, and a third half-wave voltage V.sub.3 of the same
polarity as the first half-wave voltage V.sub.1. Voltage having a
waveform made up of first to third half-wave voltages similar to
the voltage induced in the exciter coil Lex is also induced in the
primary coil L.sub.1 and the secondary coil L.sub.2 of the ignition
coil.
[0093] Although in the example illustrated in FIG. 9 the first
half-wave voltage V.sub.1 and the third half-wave voltage V.sub.3
induced in the exciter coil Lex are depicted made up of negative
voltages and the second half-wave voltage V.sub.2 is depicted made
up of positive voltage, by reversing a winding direction of the
exciter coil, the first half-wave voltage V.sub.1 and the third
half-wave voltage V.sub.3 can be made positive voltages and the
second half-wave voltage V.sub.2 can be made a negative voltage.
Similar applies to the voltage induced in the primary coil and the
secondary coil of the ignition coil.
[0094] In the present embodiment, the exciter coil Lex is wound in
the same direction as the primary coil L.sub.1 of the ignition
coil. Consequently, accompanied with rotation of the crank shaft,
voltages that are in phase with one another are induced in the
exciter coil Lex and the primary coil L.sub.1. The winding
direction of the secondary coil L.sub.2 of the ignition coil may be
freely chosen. In the present embodiment, the winding direction of
the secondary coil L.sub.2 is set so as to induce a voltage in the
secondary coil L.sub.2 that is in phase with the voltage induced in
the exciter coil Lex.
[0095] In the example illustrated in FIG. 1, at least the outer
circumferential part of the flywheel 201 attached to the crank
shaft of the engine is formed from a ferromagnetic material and the
permanent magnet 202 is attached inside the recess 203 provided in
the outer circumferential part of the flywheel 201 to configure the
magnetic field of the rotor. However, the configuration of the
magneto generator is not limited to the example illustrated in FIG.
1.
[0096] For example, in cases in which the magneto generator is
configured as an outer-magnet type magneto generator in a manner
similar to in the example illustrated in FIG. 1, a magneto rotor 2'
configured such as illustrated in FIG. 3 can be used. The magneto
rotor 2' illustrated in FIG. 3 is configured by a flywheel 210 made
of a non-magnetic material such as aluminum, a pair of permanent
magnets 211, 212 that are embedded in the flywheel 210, and
magnetic pole configuration members 213 to 215 that together with
the permanent magnets 211, 212 draw magnetic poles of the permanent
magnets 211, 212 embedded in the flywheel 210 out onto the outer
circumference of the flywheel. The magnetic pole configuration
members 213 to 215 are configured by laminated bodies made of sheet
steel, and are formed in shapes having side faces (sheet steel
lamination faces) that are disposed spaced apart by a prescribed
distance in a circumferential direction of the flywheel 210 and
outer circumferential faces (sheet steel lamination faces) that
have the same radius of curvature as the outer circumferential face
of the flywheel.
[0097] The permanent magnets 211, 212 are made of sheet-shaped
magnets that have been magnetized along thickness directions
thereof. The permanent magnets 211, 212 are disposed in a state in
which magnetic poles of one polarity (in the example illustrated, N
poles) of each magnet opposes one another in the circumferential
direction of the flywheel 210 (in a state spaced apart by a
prescribed distance in the circumferential direction of the
flywheel) and are embedded in the flywheel. The magnetic pole
configuration member 213 is disposed in a state in which one side
face 213a lies against a magnetic pole of the other polarity (in
the example illustrated, an S pole) of the permanent magnet 211 and
an outer circumferential face 213c is exposed at the outer
circumference of the flywheel 210. The magnetic pole configuration
member 213 draws a magnetic pole of the other polarity (an S pole)
of the permanent magnet 211 out onto the outer circumference of the
flywheel.
[0098] The magnetic pole configuration member 214 is embedded in
the flywheel 210 in a state disposed between the permanent magnets
211, 212 with both side faces 214a, 214b lying against the magnetic
poles of the one polarity (N poles) of the magnets 211, 212 and in
which an outer circumferential face 214c is exposed at the outer
circumference of the flywheel 210. The magnetic pole configuration
member 214 draws a magnetic pole of the one polarity (in the
example illustrated, an N pole) of the permanent magnets 211, 212
out onto the outer circumference of the flywheel.
[0099] The magnetic pole configuration member 215 is embedded in
the flywheel in a state in which one side face 215a lies against a
magnetic pole of the other polarity (in the example illustrated, an
S pole) of the permanent magnet 212 and an outer circumferential
face 215c is exposed at the outer circumference of the flywheel.
The magnetic pole configuration member 215 draws a magnetic pole of
the other polarity (in the example illustrated, an S pole) of the
permanent magnet 212 out onto the outer circumference of the
flywheel 210. At the outer circumferential part of the flywheel
210, three magnetic poles are configured by the outer
circumferential faces of the magnetic pole configuration members
213 to 215.
<Example Circuit Configuration of the Ignition Device of the
Present Embodiment>
[0100] Next, electrical configuration of the engine ignition device
of the present embodiment will be described with reference to FIG.
4.
[0101] In FIG. 4, L.sub.1 and L.sub.2 are the primary coil and the
secondary coil, respectively, of an ignition coil IG, Lex is the
exciter coil, and as previously stated, these are all provided in
the magneto generator 1 driven by the engine. In the present
embodiment, one end of the primary coil L.sub.1 of the ignition
coil is connected to the armature core 3 A and grounded, and the
primary coil L.sub.1 and the exciter coil Lex are connected to the
electronics unit 4.
[0102] The electronics unit 4 illustrated in FIG. 4 is configured
from an ignition circuit 4A, a charging circuit 4B, a microcomputer
4C which controls ignition circuit 4A and charging circuit 4B, a
power supply circuit 4D which provides a power supply voltage to
the microcomputer 4C and the like, a rotation detection circuit 4E,
and a breakdown voltage detection circuit 4F. The rotation
detection circuit 4E detects a specific feature in a waveform of
voltage induced in the exciter coil Lex and outputs a plurality of
rotation detection signals which include a rotation detection
signal generated at a reference position set at a position coming
before a crank angle position coming when a piston of the engine
reaches top dead center.
[0103] Described in further detail, the ignition circuit 4A
includes an ignition capacitor C.sub.1, a damper diode D.sub.1, and
an ignition switch SWi. One end of the ignition capacitor C.sub.1
is connected to the other end of the primary coil L.sub.1 of the
ignition coil. The damper diode D.sub.1 is connected, in parallel,
across both ends of the ignition capacitor C.sub.1 in a state in
which an anode of the damper diode D1 is pointed toward the one end
of the primary coil L.sub.1. The ignition switch SWi is provided so
as to connect the other end of the ignition capacitor C.sub.1 and
the other end of the primary coil L.sub.1. In the example
illustrated, the ignition switch SWi is configured by a MOSFET
T.sub.1. A drain of the MOSFET T.sub.1 is connected to the other
end of the ignition capacitor C.sub.1, and a source of the MOSFET
T.sub.1 is connected to the other end of the primary coil L.sub.1.
When a drive signal is being provided to a gate of the MOSFET
T.sub.1, the ignition switch SWi assumes an ON state. A parasitic
diode Df.sub.1 is formed between the drain and the source of the
MOSFET T.sub.1 configuring the ignition switch SWi.
[0104] The charging circuit 4B is configured by an NPN transistor
T.sub.2, a diode D.sub.2, a diode D.sub.3, a resistor R.sub.1, a
thyristor S.sub.1, and a diode D.sub.4. An emitter of the
transistor T.sub.2 is connected to the other end of the ignition
capacitor C.sub.1. A cathode of the diode D.sub.2 is connected to a
collector of the transistor T.sub.2, and an anode of the diode
D.sub.2 is connected to one end of the exciter coil Lex. A cathode
of the diode D.sub.3 is connected to a base of the transistor
T.sub.2. The resistor R.sub.1 is connected between the anode of the
diode D.sub.2 and an anode of the diode D.sub.3. An anode of the
thyristor S.sub.1 is connected to the anode of the diode D.sub.3,
and a cathode of the thyristor S.sub.1 is connected to an earth
line EL provided to the circuit board. An anode of the diode
D.sub.4 is connected to the earth line EL (to the cathode of the
thyristor S.sub.1), and a cathode of the diode D.sub.4 is connected
to another end of the exciter coil Lex.
[0105] In the example illustrated, a charging switch SWc is
configured by the transistor T.sub.2, the resistor R.sub.1, and the
diodes D.sub.2, D.sub.3, and a turn-OFF circuit that turns the
charging switch SWc OFF is configured by the thyristor S.sub.1.
When a second half-wave voltage V.sub.2 in the direction of the
arrow in the figure is generated in the exciter coil Lex, a base
current is provided to the transistor T.sub.2 configuring the
charging switch SWc and the transistor T.sub.2 assumes an ON state,
and when a trigger signal is provided to a gate of the thyristor
S.sub.1 and the thyristor S.sub.1 assumes an ON state, the base
current passes through the thyristor S.sub.1 bypassing the
transistor T.sub.2, whereby the transistor T.sub.2 assumes an OFF
state.
[0106] The microcomputer 4C is provided with a power supply
terminal Vcc, ports A.sub.0 to A.sub.2, an analog signal input
terminal A/D, and a CPU that has an earth terminal GND. A trigger
signal st is provided to the gate of the thyristor S.sub.1 from
port A.sub.1 of the CPU, and a drive signal (ignition signal) si is
provided to the gate of the MOSFET T.sub.1 from port A.sub.2 of the
CPU. The earth terminal GND of the CPU is connected to the earth
line EL provided to the circuit board.
[0107] The power supply circuit 4D is configured by a diode
D.sub.5, a power supply capacitor C.sub.2, a Zener diode Z.sub.1,
and a diode D.sub.6. An anode of the diode D.sub.5 is connected to
the other end of the exciter coil Lex. One end of the power supply
capacitor C.sub.2 is connected to a cathode of the diode D.sub.5
through a resistor R.sub.2, and the other end of the power supply
capacitor C.sub.2 is connected to the earth line EL. The Zener
diode Z.sub.1 is connected, in parallel, across both ends of this
capacitor, with the anode of the Zener diode Z.sub.1 pointed toward
the earth line. An anode of the diode D.sub.6 is connected to the
earth line EL, and a cathode of the diode D.sub.6 is connected to
the other end of the exciter coil Lex. The power supply circuit 4D
outputs a constant (for example, 5 V) control DC voltage that is
determined by a Zener voltage of the Zener diode Z.sub.1 as seen
from both ends of the power supply capacitor C.sub.2. A DC voltage
yielded by the power supply circuit 4D is applied across the power
supply terminal Vcc and the earth terminal GND of the CPU of the
microcomputer 4C.
[0108] The rotation detection circuit 4E includes a diode D.sub.7,
a capacitor C.sub.3, a resistor R.sub.3, an NPN transistor T.sub.3,
a resistor R.sub.5, and a resistor R.sub.6. An anode of the diode
D.sub.7 is connected to the other end of the exciter coil Lex. One
end of the capacitor C.sub.3 is connected to a cathode of the diode
D.sub.7. The resistor R.sub.3 is connected, in parallel, across
both ends of the capacitor C.sub.3. An emitter of the transistor
T.sub.3 is connected to the earth line EL, and a collector of the
transistor T.sub.3 is connected to an ungrounded output terminal of
the power supply circuit 4D through the resistor R.sub.4. The
resistor R.sub.5 is connected between a base of the transistor
T.sub.3 and the ungrounded output terminal of the power supply
circuit 4D. The resistor R.sub.6 is connected between the base of
the transistor T.sub.3 and another end of the capacitor C.sub.3.
The collector (output terminal of the rotation detection circuit)
of the transistor T.sub.3 is connected to port A.sub.0 of the
CPU.
[0109] In the illustrated rotation detection circuit 4E, an
integrating circuit is configured by the capacitor C.sub.3 and
resistors R.sub.3 and R.sub.6. The circuit constant of the
integrating circuit is set so that once the capacitor C.sub.3 has
been charged to the illustrated polarity by a first half-wave
voltage V.sub.1 and a third half-wave voltage V.sub.3 in the
direction of the dashed arrow in the figure from the exciter coil
Lex, a constant, very small voltage subsequently remains across
both ends of the capacitor C.sub.3. When the first half-wave
voltage V.sub.1 and the third half-wave voltage V.sub.3 induced in
the exciter coil Lex exceed the voltage across both ends of the
capacitor C.sub.3, a base current flows to transistor T.sub.3, the
transistor T.sub.3 assumes the ON state, and an electric potential
at the collector of the transistor T.sub.3 is reduced in a stepwise
manner. Because base current ceases to flow to the transistor
T.sub.3 when the first half-wave voltage V.sub.1 and the third
half-wave voltage V.sub.3 are less than or equal to the voltage
across both ends of the capacitor C.sub.3, the transistor T.sub.3
assumes the OFF state, and the electric potential at the collector
of the transistor T.sub.3 is increased in a stepwise manner. The
integrating circuit is provided in order to prevent the transistor
T.sub.3 from assuming the ON state and generating an erroneous
signal due to noise.
[0110] As illustrated in FIG. 9(C), between the collector and the
emitter of the transistor T.sub.3 of the rotation detection circuit
4E, there is obtained a pulse waveform signal that falls from the
power supply voltage in a stepwise manner when the first half-wave
voltage V.sub.1 rises and when the third half-wave voltage V.sub.3
rises, and that rises to the power supply voltage in a stepwise
manner when the first half-wave voltage V.sub.1 falls and the third
half-wave voltage V.sub.3 falls. Each falling edge of this signal
is recognized as a rotation detection signal sn by the CPU.
[0111] The rotation detection circuit 4E used in the present
embodiment generates a rotation detection signal sn at two crank
angle positions during one rotation of the crank shaft: a crank
angle position where a first half-wave voltage V.sub.1 generated by
the exciter coil Lex rises, and a crank angle position where a
third half-wave voltage V.sub.3 generated by the exciter coil Lex
rises. In the present embodiment, of these crank angle positions,
the crank angle position where a first half-wave voltage V.sub.1
rises is used as a reference position when detecting an ignition
timing, and the rotation detection signal sn generated at this
reference position is used as a reference signal. Each time the CPU
recognizes a rotation detection signal sn, the CPU performs a
process that identifies whether or not the rotation detection
signal sn that was just generated is a reference signal, and when
the rotation detection signal sn that was just generated is
identified as being reference signal, the CPU calculates, as a
count time used for ignition timing detection Tig, the amount of
time needed for the crank shaft to rotate from the reference
position to an ignition position at the current speed of the crank
shaft. The CPU counts down the count time used for ignition timing
detection Tig with a timer, and when the timer has finished
counting down, the CPU provides a drive signal to the ignition
switch SWi.
[0112] The breakdown voltage detection circuit 4F includes a diode
D.sub.8, a diode D.sub.9, a capacitor C.sub.4, and a resistor
R.sub.9. The diode D.sub.8 is connected between the earth line EL
and the tap B led out from a point where the first secondary coil
L.sub.21 and the second secondary coil L.sub.22 is connected, with
an anode of the diode D.sub.8 being pointed toward the earth line.
An anode of the diode D.sub.9 is connected to the tap B. One end of
the capacitor C.sub.4 is connected to a cathode of the diode
D.sub.9 through a resistor R.sub.7, and another end of the
capacitor C.sub.4 is connected to the earth line EL. The resistor
R.sub.9 is connected, in parallel, across both ends of the
capacitor C.sub.4 through a resistor R.sub.8.
[0113] The breakdown voltage detection circuit 4F generates, across
both ends of the resistor R.sub.9, a DC voltage signal Vb that is
substantially equivalent to a peak value of a voltage that appears
across both ends of the second secondary coil L.sub.22 of the
ignition coil. The voltage signal Vb is inputted to the analog
signal input terminal A/D of the CPU as a dielectric breakdown
voltage detection signal. The CPU of the microcomputer 4C detects,
as a voltage (breakdown voltage) across a discharge gap of the
ignition plug in a state in which insulation thereacross has been
broken down, a voltage signal Vb that is detected across both ends
of the second secondary coil L.sub.22 when a first spark discharge
is produced in the ignition plug as a result of a high voltage used
for ignition induced in the secondary coil of the ignition coil by
discharging the ignition capacitor C.sub.1. The breakdown voltage
takes on a low value when the stroke of the engine is an exhaust
stroke and pressure in the cylinder is low, and the dielectric
breakdown voltage takes on a high value when the stroke of the
engine is a compression stroke and pressure in the cylinder is
high.
[0114] Electronic components configuring the electronics unit 4
illustrated in FIG. 4 are mounted to the circuit board 401. One end
of the circuit board is provided with a terminal electrode a,
terminal electrodes b and c, a terminal electrode d, a terminal
electrode e, and a terminal electrode f. The terminal electrode a
is connected to the one end of the ignition capacitor C.sub.1. The
terminal electrodes b and c are connected to the earth line EL. The
terminal electrode d is connected to the cathode of the diode
D.sub.4. The terminal electrode e is connected to the cathode of
the diode D.sub.6. The terminal electrode f is connected to the
anode of the diode D.sub.9. When the stator 3 of the magneto
generator is assembled, the terminal electrodes b and c are
respectively connected to the armature core 3A and a ground
terminal C of the secondary coil, these being parts at a ground
potential. The primary coil L.sub.1 of the ignition coil is
connected between the terminal electrode a and the terminal
electrode b, and the exciter coil Lex is connected between the
terminal electrode d and the terminal electrode e. The ungrounded
terminal A of the secondary coil L.sub.2 of the ignition coil is
connected to the ungrounded terminal of the ignition plug P through
a high-voltage cord.
[0115] The ignition device illustrated in FIG. 4 is controlled by
executing a prescribed program using the CPU of the microcomputer
4C. As illustrated in FIG. 7, in addition to the CPU, ROM, and RAM,
the microcomputer 4C is provided with a timer 0, a timer 1, and a
timer 2. Output from the rotation detection circuit 4E is inputted
to port A.sub.0 of the CPU, and output from the breakdown voltage
detection circuit 4F is inputted to the analog signal input
terminal A/D of the CPU. Trigger signals are provided from port
A.sub.1 of the CPU to the thyristor S.sub.1 configuring the circuit
that turns the charging switch SWc OFF, and drive signals are
provided from port A.sub.2 of the CPU to the gate of the MOSFET
T.sub.1 configuring the ignition switch SWi.
[0116] Of the timers 0 to 2, timer 0 is used in order to count down
a time Ty for insulation across the discharge gap of the ignition
plug P to reach a broken down state after a drive signal has been
provided to the ignition switch SWi at an ignition timing, and
timer 1 is used in order to count down a time Tig for detecting an
ignition timing.
[0117] Timer 2 counts time between when rotation detection signals
sn are generated by the rotation detection circuit 4E. Timer 2 is
controlled by the CPU so as to repeatedly reset and resume a timing
operation each time a rotation detection signal sn is generated. As
illustrated in FIG. 9(C), using a count value from timer 2 read
immediately before resetting timer 2, the CPU detects a time Txa
from when a rotation detection signal sn is generated at a rising
edge of a first half-wave voltage V.sub.1 outputted by the exciter
coil to when a rotation detection signal sn is generated at a
rising edge of a third half-wave voltage V.sub.3 outputted by the
exciter coil, and the CPU detects a time Txb from when a rotation
detection signal sn is generated at a rising edge of the third
half-wave voltage V.sub.3 to when a rotation detection signal sn is
generated at a rising edge of the next first half-wave voltage
V.sub.1.
<Functional Means Configured by the CPU>
[0118] The microcomputer 4C configures various functional means by
executing a prescribed program stored in the ROM using the CPU. In
order to implement the ignition method of the present invention,
the microcomputer 4C performs control of the charging switch SWc
that flows a charging current to the ignition capacitor C.sub.1 and
performs control of the ignition switch SWi that discharges the
ignition capacitor C.sub.1.
[0119] FIG. 8 is a block diagram that uses various functional means
configured by the microcomputer 4C to express a configuration of
the ignition device of FIG. 4. In the present embodiment, the CPU
executes the prescribed program stored in the ROM, and thereby
configures a reference signal identification means 41, an ignition
timing calculation means 42, a stroke discrimination means 43, a
timer 1 setting means 44, an ignition signal generation means 45, a
switch turn-ON means 46, a timer 0 setting means 48, and a switch
turn-OFF means 49.
[0120] In FIG. 8, the reference signal identification means 41
reads a count value from timer 2 each time a rotation detection
signal sn is generated by the rotation detection circuit 4E, and
when the count value from timer 2 that was just read is greater
than the count value from timer 2 read when a rotation detection
signal was last generated, the reference signal identification
means 41 identifies the rotation detection signal that was just
generated as a reference signal generated at a rising edge of a
first half-wave voltage. The reference signal identification means
41, for example, identifies a rotation detection signal sn read at
moment t.sub.4 in FIG. 9(C) as a reference signal due to the count
value Txb read at moment t.sub.4 being larger than the count value
Txa that was last read before that. A reference signal is generated
only once during one rotation of the crank shaft. In the present
embodiment, the crank angle position when the reference signal is
generated is used as a reference position at which timer 1 is
caused to begin counting down a count time used for ignition timing
detection Tig.
[0121] The ignition timing calculation means 42 detects a time Tx
(=Txa+Txb) needed for the crank shaft make one rotation based on a
count value from timer 2, which repeatedly resets and resumes a
timing operation each time a rotation detection signal is detected,
determines an angle .theta.x from a crank angle position (reference
position) where a reference signal is detected to a crank angle
position where ignition of the engine is performed using
information relating to engine speed obtained from this time Tx,
and calculates, as a count time used for ignition timing detection
Tig, the amount of time needed for the crank shaft to rotate the
angle .theta.x from the reference position at the current speed of
the crank shaft.
[0122] The stroke discrimination means 43 makes use of the fact
that the breakdown voltage (voltage across the discharge gap of the
ignition plug in a state that insulation across the discharge gap
is broken down) detected through the breakdown voltage detection
circuit 4F from partway along the secondary coil L.sub.2 when a
first spark discharge is produced in the ignition plug as a result
of a high voltage induced in the secondary coil of the ignition
coil by discharging the ignition capacitor C.sub.1 when the
ignition switch SWi is placed into the ON state differs between
when the stroke of the engine is an exhaust stroke and when the
stroke of the engine is a compression stroke, and thereby
discriminates whether a stroke of the engine is an exhaust stroke
or a compression stroke when each reference signal is
generated.
[0123] Because the breakdown voltage of the discharge gap of the
ignition plug when the stroke of the engine is a compression stroke
is higher than the breakdown voltage when the stroke of the engine
is an exhaust stroke, it is possible to discriminate whether a
stroke for which a reference signal has been detected is a
compression stroke or an exhaust stroke by performing a voltage
determination procedure that compares the breakdown voltage
detected when a first spark discharge is produced in the ignition
plug at an ignition timing with the breakdown voltage detected when
a first spark discharge was produced in the ignition plug at the
previous ignition timing.
[0124] In order to reliably discriminate between strokes, it is
preferable that the stroke discrimination means 43 be configured so
as to ultimately determine whether a stroke for which a reference
signal has been detected is a compression stroke or an exhaust
stroke based on results from performing the aforementioned voltage
determination procedure multiple times. In cases in which the
engine is a four-cycle engine, the detection of a reference signal
generated in a compression stroke and the detection of a reference
signal generated in an exhaust stroke are alternatingly performed
in accompaniment with rotation of the crank shaft. Thus, if stroke
discrimination by the stroke discrimination means 43 is performed
immediately after starting the engine, stroke discrimination can be
performed in a mechanical manner thereafter.
[0125] The timer 1 setting means 44 sets a count time Tig used for
ignition timing detection to timer 1 and causes timer 1 to begin
counting down the time Tig set thereto. Immediately after starting
the engine, when the stroke discrimination means 43 is in a state
in which stroke discrimination is not yet finished, each time a
reference signal is generated and the ignition timing calculation
means 42 calculates a count time Tig used for ignition timing
detection, the timer 1 setting means 44 sets this count value Tig
to timer 1 and causes timer 1 to begin counting down, and after the
stroke discrimination means 43 has finished the stroke
discrimination, the timer 1 setting means 44 sets a count value
used for ignition timing detection Tig to timer 1 and causes timer
1 to begin counting down only in cases in which stroke of the
engine when a reference signal has been generated is a compression
stroke.
[0126] The ignition signal generation means 45 generates an
ignition signal when timer 1 has finished counting down a count
value Tig set thereto, and the switch turn-ON means 46 provides a
drive signal to the MOSFET T.sub.1 and places the ignition switch
SWi into the ON state when an ignition signal is generated.
[0127] In the present embodiment, the ignition timing calculation
means 42, the timer 1 setting means 44, timer 1, and the ignition
signal generation means 45 configure an ignition timing detection
means 47 that generates an ignition signal when an ignition timing
of the engine is detected.
[0128] The timer 0 setting means 48 sets a preset time Ty to timer
0 and causes timer 0 to begin counting down. The time Ty is the
time until a first spark discharge is produced across the discharge
gap of the ignition plug and the insulation across the discharge
gap of the ignition plug reaches a broken down state after an
ignition signal has been provided to the ignition switch SWi. The
time Ty is set to an appropriate value ahead of time on the basis
of a result of tests that count an amount of time until a first
spark discharge is produced in the ignition plug after an ignition
signal has been provided to the ignition switch SWi.
[0129] The switch turn-OFF means 49 places the ignition switch SWi
and the charging switch SWc into the OFF state when timer 0 has
finished counting down a time Ty set thereto. When timer 0 has
finished counting down a time Ty set thereto, the switch turn-OFF
means 49 places the MOSFET T.sub.1 into the OFF state by removing
the drive signal that had been provided to the MOSFET T.sub.1 and
places the transistor T.sub.2 in the OFF state by providing a
trigger signal to the thyristor S.sub.1. Thereby, in a state in
which current does not flow to the primary coil L.sub.1 of the
ignition coil and the exciter coil Lex and the occurrence of
armature reaction in the magneto generator is prevented, a voltage
induced in the secondary coil of the ignition coil due to a change
in magnetic flux inputted to the armature core from the magneto
rotor is applied to the ignition plug P in a state in which the
insulation across the discharge gap has been broken down due to a
first spark discharge, and a second spark discharge is produced in
the ignition plug P.
<Operation of the Ignition Device of the Present
Embodiment>
[0130] Operation of the ignition device illustrated in FIG. 4 will
now be described with reference to FIG. 9. FIG. 9 is a timing chart
illustrating operation of the present embodiment in a state after
engine stroke discrimination has finished. The horizontal axis in
FIG. 9 indicates time t (sec). The symbols EXH, INT, COM, and EXP
shown in the upper part of FIG. 9 respectively indicate when the
stroke of the engine is an exhaust stroke, an intake stroke, a
compression stroke, and a power stroke. Further, the "(CA)" in
"360.degree. (CA)" means crank angle, and TDC and BTDC respectively
indicate a top dead center and a bottom dead center of the
piston.
[0131] FIG. 9(A) illustrates changes in magnetic flux .phi.
produced in the armature core accompanying rotation of the magneto
rotor. FIG. 9(B) illustrates a waveform of voltage induced in the
exciter coil Lex accompanied with changes in the magnetic flux
.phi. when under no load. Due to this change in the magnetic flux
.phi., the exciter coil generates a voltage having an AC waveform
in which a first half-wave voltage V.sub.1, a second half-wave
voltage V.sub.2 of a different polarity to that of the first
half-wave voltage, and a third half-wave voltage V.sub.3 of the
same polarity as the first half-wave voltage V.sub.1 sequentially
appear at a position coming before a top dead center position (a
crank angle position coming when the piston reaches top dead
center) of an exhaust stroke and at a position coming before the
top dead center position of a compression stroke. These voltages
appear one time each during one rotation of the crank shaft. The
positions at which the exciter coil generates voltage can be
adjusted, as appropriate, according to a position where the stator
is attached to the magneto generator.
[0132] In the ignition device illustrated in FIG. 4, a base current
is provided to the transistor T.sub.2 when the exciter coil Lex
generates a second half-wave voltage V.sub.2 and this transistor
assumes the ON state. Accordingly, while the exciter coil Lex is
generating a second half-wave voltage V.sub.2, the ignition
capacitor C.sub.1 is charged to the illustrated polarity through
the route: exciter coil Lex.fwdarw.diode D.sub.2.fwdarw.transistor
T.sub.2.fwdarw.ignition capacitor C.sub.1.fwdarw.primary coil
L.sub.1.fwdarw.diode D.sub.4.fwdarw.exciter coil Lex, and the
voltage Vc across both ends of the ignition capacitor C.sub.1
changes as in FIG. 9(F).
[0133] When the exciter coil Lex generates voltage, a signal with a
waveform such as illustrated in FIG. 9(C) is inputted to the CPU
from the rotation detection circuit 4E. Of the signal provided from
the rotation detection circuit 4E, the CPU respectively recognizes
falling edges that occur at moments t.sub.1, t.sub.4, . . . and
falling edges that occur at moments t.sub.3, t.sub.8, . . . as
rotation detection signals sn, and of these rotation detection
signals, the CPU identifies the rotation detection signals sn
occurring when a first half-wave voltage V.sub.1 rises at moments
t.sub.1, t.sub.4, . . . as reference signals.
[0134] When the engine stroke discrimination is finished, the CPU
sets a count time used for ignition timing detection Tig to timer 1
and causes timer 1 to begin counting down when a reference signal
is generated at moment t.sub.4 in a compression stroke of the
engine, and the CPU generates an ignition signal si and places the
ignition switch (MOSFET T.sub.1) in the ON state when timer 1
finishes counting down the time Tig at moment t.sub.6. This
discharges electric charge accumulated by the ignition capacitor C1
through the route: ignition capacitor C.sub.1.fwdarw.MOSFET
T.sub.1.fwdarw.primary coil L.sub.1.fwdarw.ignition capacitor
C.sub.1. This discharge induces a high voltage used for ignition in
the secondary coil L.sub.2 of the ignition coil and produces a
first spark discharge in the ignition plug P.
[0135] After the ignition capacitor C.sub.1 has been discharged,
the CPU terminates the ignition signal si at time t.sub.7 (see FIG.
9E), which is when the extremely small amount of moment Ty, which
is from when a first spark discharge was produced to when the
insulation across the discharge gap of the ignition plug reaches a
broken down state, has elapsed, and the CPU stops suppling a drive
signal to the MOSFET T.sub.1 (ignition switch), whereby at the same
time as placing the MOSFET T.sub.1 in the OFF state and preventing
current flow to the primary coil through the route: primary coil
L.sub.1.fwdarw.damper diode D.sub.1.fwdarw.MOSFET
T.sub.1.fwdarw.primary coil L.sub.1, the CPU provides a trigger
signal st (see FIG. 9D) to the thyristor S.sub.1 and places the
thyristor in the ON state, which places the transistor T.sub.2
(charging switch) in the OFF state and prevents current flow to the
exciter coil Lex through the route: exciter coil Lex.fwdarw.diode
D.sub.2.fwdarw.transistor T.sub.2.fwdarw.MOSFET
T.sub.1.fwdarw.diode D.sub.4.fwdarw.exciter coil Lex and through
the route: exciter coil Lex.fwdarw.diode D.sub.2.fwdarw.transistor
T.sub.2.fwdarw.capacitor C.sub.1.fwdarw.primary coil
L.sub.1.fwdarw.diode D.sub.4.fwdarw.exciter coil Lex. Thereby, in a
state in which the occurrence of armature reaction in the magneto
generator caused by current flow through the primary coil and
current flow through the exciter coil is prevented, a voltage
induced in the secondary coil L.sub.2 due to a change in magnetic
flux that is inputted to the armature core from the magneto rotor
is applied to the ignition plug P in a state in which the
insulation thereacross has been broken down due to a first spark
discharge, whereby a second spark discharge is produced in the
ignition plug P.
[0136] FIGS. 9(G), (H), and (I) schematically illustrate respective
waveforms of a primary current ig.sub.1, a secondary voltage
Vg.sub.2, and a secondary current ig.sub.2 in the ignition coil. Of
the parts of the waveform of the secondary voltage Vg.sub.2 in the
ignition coil illustrated in FIG. 9(H), the portion indicated by
symbol V.sub.2a is a waveform of high voltage used for ignition in
an oscillating waveform produced by discharging the ignition
capacitor, and the portion indicated by symbol V.sub.2b is a
waveform of a secondary voltage when an output voltage of the
magneto generator is being induced in the secondary coil of the
ignition coil. Of the parts of the waveform of the secondary
current illustrated in FIG. 9(I), the portion indicated by symbol
i.sub.2a is a waveform of a discharge current that flows while a
first spark discharge is being produced, and the portion indicated
by symbol i.sub.2b is a waveform of a discharge current that flows
when an output voltage of the magneto generator is being applied to
the ignition plug from the secondary coil of the ignition coil.
[0137] In conventional capacitor discharge ignition devices,
because ignition of the engine is due only to a spark discharge
produced when a voltage V.sub.2a, which is produced when the
ignition capacitor has been discharged, is applied to the ignition
plug, the duration of spark discharges are extremely short and
ignition energy may be insufficient. However, with the present
invention, because a voltage V.sub.2b is generated following a
voltage V.sub.2a and a second spark discharge is produced, the
duration of ignition sparks can be made longer and ignition energy
can be increased.
[0138] The stroke discrimination means 43 makes use of the fact
that the breakdown voltage across the discharge gap of the ignition
plug detected through the breakdown voltage detection circuit 4F
from partway along the secondary coil L.sub.2 of the ignition coil
when a first spark discharge is produced differs between an exhaust
stroke and a compression stroke, and thereby performs a process
that discriminates whether a stroke of the engine is a compression
stroke or an exhaust stroke. Because it takes a certain amount of
time for this process to finish after the engine is started, in the
present embodiment, when the engine is started, ignition is
performed not only at a regular ignition position set in the
vicinity of a top dead center position of a compression stroke, but
also at an ignition position set in the vicinity of a top dead
center position of an exhaust stroke. After a certain amount of
time has elapsed after the engine is started and the process that
discriminates whether the stroke of the engine is a compression
stroke or an exhaust stroke has finished, an ignition operation is
only performed at the regular ignition position set in the vicinity
of a top dead center position of a compression stroke.
[0139] In the embodiment illustrated in FIG. 4, the damper diode
D.sub.1 is provided so that after the ignition capacitor C.sub.1
has been discharged, a series resonance circuit that discharges the
capacitor C.sub.1 is not formed on a primary side of the ignition
coil after the ignition capacitor C.sub.1 is charged in an opposite
direction. The damper diode D1 is also provided in order to
lengthen an interval of an initial half-wave of high voltage
induced in the secondary coil L.sub.2 of the ignition coil after
the ignition capacitor is discharged, and to lengthen the duration
of the first spark discharge. This is done by releasing, over time,
energy accumulated by the primary coil L.sub.1 of the ignition coil
through the diode D.sub.1 and the MOSFET T.sub.1.
[0140] The configuration of the electrical circuit of the ignition
device according to the present invention is not limited to the
example illustrated in FIG. 4. FIG. 5 illustrates another example
circuit configuration of the ignition device according to the
present invention. In this example, the power supply circuit 4D and
the rotation detection circuit 4E have configurations that differ
from the example illustrated in FIG. 4. Further, the exciter coil
Lex is made up of a pair of coils Lex.sub.1 and Lex.sub.2 that are
wound in the same direction and connected to one another in
parallel, and the secondary coil L.sub.2 and the exciter coil Lex
are connected in series.
[0141] The power supply circuit 4D illustrated in FIG. 5 is
configured by a diode D.sub.5, a capacitor C.sub.5, a diode
D.sub.6, a Zener diode Z.sub.2, a diode D.sub.10, a power supply
capacitor C.sub.2, and a Zener diode Z.sub.1. An anode of the diode
D.sub.5 is connected to the earth line EL. One end of the capacitor
C.sub.5 is connected to a cathode of the diode D.sub.5. The diode
D.sub.6 is connected between the other end of the capacitor C.sub.5
and the anode of the diode D.sub.2, with an anode of the diode
D.sub.6 being pointed toward the capacitor C.sub.5. The Zener diode
Z.sub.2 is connected, in parallel, across both ends of the
capacitor C.sub.5, with a cathode of the Zener diode Z.sub.2 being
pointed toward the diode D.sub.5. An anode of the diode D.sub.10 is
connected to a point where the capacitor C.sub.5 and the cathode of
the diode D.sub.5 is connected. The power supply capacitor C.sub.2
is connected between the cathode of the diode D.sub.10 and the
earth line EL. The Zener diode Z.sub.1 is connected, in parallel,
across both ends of the power supply capacitor C.sub.2, with an
anode of the Zener diode Z.sub.2 pointed toward the earth line.
[0142] In the power supply circuit 4D illustrated in FIG. 5, the
capacitor C.sub.5 is charged to the illustrated polarity when the
exciter coil Lex generates a first half-wave voltage V.sub.1 and
when the exciter coil Lex generates a third half-wave voltage
V.sub.3, and the power supply capacitor C.sub.2 is charged to the
illustrated polarity by the voltage across both ends of the
capacitor C.sub.5.
[0143] In the rotation detection circuit 4E illustrated in FIG. 5,
a diode D.sub.11 is connected between the base and the emitter of
the transistor T.sub.3 with an anode of the diode D.sub.11 being
connected to the earth line EL. An integrating circuit is also
connected between the base of the transistor T.sub.3 and a line
tied to a terminal of the exciter coil Lex on the opposite side of
the exciter coil Lex to the secondary coil L.sub.2. This
integrating circuit is configured by the series connection of a
resistor R.sub.6, a parallel circuit having a capacitor C.sub.3 and
a resistor R.sub.3, and a diode D.sub.7 configured having an anode
thereof pointed toward the parallel circuit.
[0144] In the example illustrated in FIG. 5, one end of the circuit
board 401 is formed with a terminal electrode a, terminal
electrodes b and d, a terminal electrode f, and a terminal
electrode e. The terminal electrode a is tied to the one end of the
ignition capacitor C.sub.1. The terminal electrodes b and d are
connected to the earth line EL. The terminal electrode f is
connected to the anode of the diode D.sub.9. The terminal electrode
e is connected to a line tied to the anode of the diode D.sub.2 of
the charging circuit. The primary coil L.sub.1 of the ignition coil
is connected between the terminal electrodes a and b. The terminal
electrode b is connected to the armature core 3A, which is a part
at the ground potential, and the exciter coil Lex is connected
between the terminal electrodes d and e. The terminal electrode f
is connected to the tap B of the secondary coil of the ignition
coil. Through the tap B, a voltage from partway along the secondary
coil L.sub.2 is inputted to the dielectric breakdown voltage
detection circuit 4F. Other configuration of the embodiment
illustrated in FIG. 5 is the same as in the embodiment illustrated
in FIG. 4.
[0145] In the rotation detection circuit 4E illustrated in FIG. 5,
when the exciter coil Lex is not generating a first half-wave
voltage V.sub.1 and a third half-wave voltage V.sub.3, the
transistor T.sub.3 assumes the ON state due to a base current that
is provided from the power supply circuit 4D to the transistor
T.sub.3 through the resistor R.sub.5, and the electric potential at
the collector of the transistor T.sub.3 is at roughly the ground
potential. While a first half-wave voltage V.sub.1 and a third
half-wave voltage V.sub.3 generated by the exciter coil Lex exceed
the voltage across both ends of the capacitor C.sub.3, current
flows through the diode D.sub.11, and due to the voltage across
both ends of the diode D.sub.11 dropping, the transistor T.sub.3
assumes the OFF state and the voltage between the collector and the
emitter of the transistor T.sub.3 is increased. Consequently,
between the collector and the emitter of the transistor T.sub.3,
there is obtained a signal that rises to about the power supply
voltage in a stepwise manner when a first half-wave voltage V.sub.1
and a third half-wave voltage V.sub.3 have risen and that falls in
a stepwise manner when the first half-wave voltage V.sub.1 and the
third half-wave voltage V.sub.3 have fallen. The CPU recognizes
rising edges in this signal as rotation detection signals sn, and
recognizes rotation detection signals occurring at a rising edge of
a first half-wave voltage V.sub.1 as reference signals. Other
features are the same as in the embodiment illustrated in FIG.
4.
[0146] When the exciter coil Lex is configured by a pair of coils
Lex.sub.1 and Lex.sub.2 that are wound in the same direction and
connected to one another in parallel as described above, loss in
the circuit that charges the ignition capacitor C.sub.1 is reduced,
enabling the ignition capacitor to be charged to a higher
voltage.
[0147] FIG. 6 illustrates another example configuration of the
ignition device according to the present invention. In this
example, the ignition circuit 4A and the charging circuit 4B have
configurations that differ from the example illustrated in FIG. 4
and the example illustrated in FIG. 5. The ignition circuit 4A
illustrated in FIG. 6 includes an ignition capacitor C.sub.1, a
MOSFET T.sub.1 and a damper diode D.sub.1. One end of the ignition
capacitor C.sub.1 is connected to the one end of the primary coil
L.sub.1. A drain of the MOSFET T.sub.1 is connected to another end
of the ignition capacitor C.sub.1, and a source of the diode
D.sub.1 is connected to the earth line EL. The damper diode D.sub.1
is connected across both ends of the ignition capacitor C.sub.1.
The charging circuit 4B includes a diode D.sub.2 and a MOSFET
T.sub.2. An anode of the diode D.sub.2 is connected to one end of
the exciter coil Lex, and a cathode of the diode D.sub.2 is
connected to the one end of the ignition capacitor C.sub.1. A drain
of the MOSFET T.sub.2 is connected to the other end of the ignition
capacitor C1, and a source of the MOSFET T.sub.2 is connected to
the earth line EL. A parasitic diode Df.sub.2 is formed between the
drain and the source of the MOSFET T.sub.2. Other features are
configured the same as in the example illustrated in FIG. 5.
[0148] In the example illustrated in FIG. 6, one end of the circuit
board 401 is formed with a terminal electrode a, a terminal
electrode b, a terminal electrode d, a terminal electrode f, and a
terminal electrode e. The terminal electrode a is tied to the one
end of the ignition capacitor C.sub.1. The terminal electrode b is
connected to the drain of the MOSFET T.sub.1. The terminal
electrode d is connected to the earth line EL. The terminal
electrode f is connected to the anode of the diode D.sub.9. The
terminal electrode e is connected to a line tied to the anode of
the diode D.sub.2 of the charging circuit. The primary coil L.sub.1
of the ignition coil is connected between the terminal electrodes a
and b. The terminal electrode d is connected to the armature core
3A, which is a part at the ground potential, and is connected to a
point C where the exciter coil Lex and the secondary coil L.sub.2
connect. The terminal electrode e is connected to a terminal D of
the exciter coil Lex on the opposite side of the exciter coil Lex
to the secondary coil L.sub.2.
[0149] In the embodiment illustrated in FIG. 6, the CPU provides a
drive signal st to the MOSFET T.sub.2 when a reference signal is
generated at moments t.sub.1, t.sub.4, . . . depicted in FIG. 9.
The MOSFET T.sub.2 assumes the ON state when a second half-wave
voltage V.sub.2 is generated by the exciter coil Lex at moments
t.sub.2 and t.sub.5, and a charging current flows to the ignition
capacitor C.sub.1 through the route: exciter coil Lex.fwdarw.diode
D.sub.2.fwdarw.ignition capacitor C.sub.1.fwdarw.MOSFET
T.sub.2.fwdarw.exciter coil Lex.
[0150] A drive signal is provided to the MOSFET T.sub.1 when the
CPU generates an ignition signal si at an ignition timing. This
MOSFET therefore assumes the ON state, and electric charge
accumulated by the ignition capacitor C.sub.1 is discharged through
the route: ignition capacitor C.sub.1.fwdarw.primary coil
L.sub.1.fwdarw.MOSFET T.sub.1.fwdarw.MOSFET
T.sub.2.fwdarw.parasitic diode Df.sub.2.fwdarw.ignition capacitor
C.sub.1. Thereby, a high voltage is induced in the secondary coil
of the ignition coil and a first spark discharge is generated in
the ignition plug. When a time Ty has elapsed from the ignition
timing, the CPU removes the ignition signal and places the MOSFET
T.sub.1 in the OFF state while at the same time removing the drive
signal that had been provided to the MOSFET T.sub.2 and placing the
MOSFET T2 in the OFF state, giving rise to a state in which current
does not flow through the primary coil L.sub.1 of the ignition coil
and the exciter coil Lex, and a voltage induced in the secondary
coil L.sub.2 due to a change in magnetic flux that is inputted to
the armature core from the magneto rotor is applied to the ignition
plug, the insulation across the discharge gap thereof having been
broken down by the first spark discharge, producing a second spark
discharge.
<Program Executed by the CPU>
[0151] The reference signal identification means 41, the ignition
timing calculation means 42, the stroke discrimination means 43,
the timer 1 setting means 44, the ignition signal generation means
45, the switch turn-ON means 46, the timer 0 setting means 48, and
the switch turn-OFF means 49 illustrated in FIG. 8 are configured
by executing a program stored in the ROM of the microcomputer using
the CPU.
[0152] FIGS. 10 to 16 depict flowcharts illustrating algorithms of
the program executed by the CPU in order to configure the
functional means illustrated in FIG. 8. FIG. 10 is a flowchart that
broadly illustrates a flow of processes executed after the
microcomputer has been powered on. FIG. 11 is a flowchart that
illustrates a flow of an initialization process executed first
after the microcomputer has been powered on. FIG. 12 is a flowchart
illustrating an algorithm for a main process executed after the
initialization process has finished. FIG. 13 is a flowchart
illustrating an algorithm for a rotation detection signal interrupt
process executed each time the rotation detection circuit 4E
generates a rotation detection signal. FIG. 14 is a flowchart
illustrating a flow of a timer 1 interrupt process executed when
timer 1 has finished counting down a time Tig set thereto. FIG. 15
is a flowchart illustrating part of a flow of a timer 0 interrupt
process executed when timer 0 has finished counting down a time Ty
set thereto. FIG. 16 is a flowchart illustrating the rest of the
flow of the timer 0 interrupt process.
[0153] In cases in which the algorithms illustrated in FIGS. 10 to
16 are followed, an engine start operation is performed, and when
the microcomputer has been powered on, first, at step S001 in FIG.
10, an initialization process (FIG. 11) is performed for each part
of the microcomputer, and when the initialization process has
finished the main process (FIG. 12) illustrated in step S002 of
FIG. 10 is performed.
[0154] In the initialization process illustrated in FIG. 11, first,
at step S101, the ports and various internal functions of the CPU
are initialized, and then, at step S102, the ignition switch SWi is
placed into an open state (OFF state). The initialization process
then proceeds to step S103, where the charging switch SWc is placed
into a state able to be turned ON. This is a state provided with a
drive signal so that the charging switch SWc will immediately turn
ON if a voltage is applied across both ends thereof. At step S103,
a drive signal is provided to a switch element (transistor T.sub.2
in the examples illustrated in FIGS. 4 and 5, MOSFET T.sub.2 in the
example illustrated in FIG. 6) configuring the charging switch SWc,
and the charging switch SWc is placed into a state able to be
immediately turned ON if a voltage is applied to the charging
switch SWc. Then, at step S104, a [calculation permitted flag] is
cleared to 0, and at step S105, a [stroke discrimination finished
flag] is cleared to 0. At step S106, a [stroke flag] is cleared to
0, and at step S107, a [stroke discrimination byte] is set to [0000
0000]. Then, at step S108, other user memory is initialized, and at
step S109, timer 2 is started, after which the initialization
process ends.
[0155] After the initialization process of FIG. 11 has ended, the
main process of FIG. 12 is performed. In the main process, first,
at step S201, a watchdog timer is cleared, and at step S202, a
determination is made as to whether or not the [calculation
permitted flag] is set to 1. As a result thereof, the main process
returns to step S201 when it has been determined that the
[calculation permitted flag] is not set to 1, and when it has been
determined that the [calculation permitted flag] is set to 1, the
[calculation permitted flag] is cleared to 0 at step S203.
Afterwards, at step S204, information relating to the speed of the
engine included in the previous count value Tx-1 from timer 2 read
each time a rotation detection signal sn is generated is used to
perform a calculation that determines an angle .theta.x from a
crank angle position (reference position) to where a reference
signal was generated to an ignition position, which is a crank
angle position where engine ignition is performed. The angle
.theta.x is, for example, determined by referring to a map that
correlates Tx-1 and .theta.x and performing a complementary
calculation.
[0156] The rotation detection signal interrupt process illustrated
in FIG. 13 is performed each time a rotation detection signal sn is
generated. In this interrupt process, first, at step S301, a count
value (Txa or Txb illustrated in FIG. 9C) from timer 2 is read and
stored in memory as [Tx], and after being reset, timer 2 is
restarted. Then, at step S302, it is identified whether or not the
most recent rotation detection signal sn is a reference signal.
This identification is performed by making a determination as to
whether or not the count value from the timer that was just read is
greater than the count value from timer 2 that was read when a
rotation detection signal was last generated before that. In other
words, when the count value from the timer 2 that was just read is
greater than the count value from timer 2 that was last read before
that (when the count value that was just read is Txb), the rotation
detection signal that was just generated is identified as a
reference signal generated at a rising edge of a first half-wave
voltage.
[0157] At step S302, when, as a result of performing the
identification as to whether or not the most recent rotation
detection signal sn is a reference signal, it has been determined
that the rotation detection signal sn is not a reference signal,
nothing more is done and the program exits this process. When at
step S302 the most recent rotation detection signal sn has been
identified as a reference signal, the interrupt process proceeds to
step S303 and the [calculation permitted flag] is set to 1. Then,
at step S304, the .theta.x calculated in the main process and the
Tx that stored in memory at step S301 are used to calculate, as a
count time used for ignition timing detection Tig, the amount of
time needed to rotate the angle .theta.x (to the ignition position)
from the crank angle position (the current crank angle position)
where the reference signal was generated. Then, at step S305, the
count time used for ignition timing detection Tig is set to timer 1
and timer 1 is immediately made to begin counting down, after which
the program returns to the main process.
[0158] The timer 1 interrupt process illustrated in FIG. 14 is
performed when timer 1 has finished counting down the count value
Tig set thereto. In this interrupt process, at step S401, a
determination is made as to whether or not a [stroke discrimination
completion flag] is set to 1 (a determination is made as to whether
or not a stroke discrimination process has finished). In cases in
which, as a result thereof, it has been determined that the [stroke
discrimination completion flag] is set to 1 (that the stroke
determination process has finished), the interrupt process proceeds
to step S402 and a determination is made as to whether or not the
[stroke flag] is set to 1 (a determination is made as to whether or
not the current stroke is a compression stroke). In cases in which,
as a result thereof, it has been determined that the [stroke flag]
is set to 1 (that the current stroke is a compression stroke), the
interrupt process proceeds to step S403 and the [stroke flag] is
cleared to 0. Then, at step S404, an ignition signal is generated
and the ignition switch is placed into the ON state, which
discharges the ignition capacitor C.sub.1 and produces a first
spark discharge in the ignition plug. Then, at step S405, timer 0
is set to the time Ty, after which the program exits this process.
The time Ty is the amount of time needed for the insulation across
the discharge gap of the ignition plug to reach a broken down state
after an ignition signal is generated and the ignition capacitor
C.sub.1 begins to discharge. In cases in which, at step S402, it
has been determined that the [stroke flag] is not set to 1 (that
the stroke determination process is not yet finished), the
interrupt process proceeds to step S406 and the [stroke flag] is
set to 1, after which the program returns to the main process.
[0159] The timer 0 interrupt process illustrated in FIGS. 15 and 16
is performed when, after the ignition capacitor C.sub.1 has been
discharged, timer 0 has finished counting down the count value Ty
set thereto. In this interrupt process, first, at step S501 in FIG.
15, the charging switch SWc is placed into the OFF state (open
state), and then, at step S502, the ignition switch SWi is placed
into the OFF state. Then, at step S503, a determination is made as
to whether or not the [stroke discrimination completion flag] is
set to 1 (a determination is made as to whether or not stroke
discrimination has finished). When, as a result thereof, it has
been determined that the [stroke discrimination completion flag] is
not set to 1 (that stroke discrimination is not finished), the
interrupt process proceeds to step S504 and a determination is made
as to whether or not the current process is an initial process.
When in this determination it has been determined that the current
process is an initial process, the interrupt process proceeds to
step S505, a signal outputted by the breakdown voltage detection
circuit 4F is read from an A/D input terminal of the CPU, and after
storing a value that has been read as [Output NEW], the program
exits this process.
[0160] When at step S504 it has been determined that the current
process is not an initial process, the interrupt process proceeds
to step S506 in FIG. 16 and the content of [Output NEW] is stored
as [Output OLD]. Then, at step S507, data that has been inputted to
the A/D input terminal of the CPU is stored as [Output NEW]. Then,
the interrupt process proceeds to step S508, and after multiplying
the [stroke discrimination byte] by 2 (after shifting the [stroke
discrimination byte] to the left), the interrupt process proceeds
to step S509 and [Output NEW] and [Output OLD] are compared. When,
as a result thereof, it has been determined that [Output
NEW].gtoreq.[Output OLD], the interrupt process proceeds to step
S510 and the [stroke discrimination byte] is incremented, and at
step S511 a determination is made as to whether or not the [stroke
discrimination byte] matches [1010 1010]. When, as a result of this
determination, it has been determined that the [stroke
discrimination byte] does not match [1010 1010], nothing more is
done and the program exits this process. When at step S511 it has
been determined that the [stroke discrimination byte] matches [1010
1010], the interrupt process proceeds to step S512 and the [stroke
flag] is set to 1 so that the stroke of the engine is determined to
be a compression stroke the next time the timer 0 interrupt process
is performed. Then the [stroke discrimination completion flag] is
set to 1 in order to indicate that the stroke discrimination
process has finished and the program exits this process.
[0161] With the algorithms illustrated in FIGS. 10 to 16, the
reference signal identification means 41 is configured by a
procedure that performs step S302 of the process of FIG. 13, and
the ignition timing calculation means 42 is configured by a
procedure that performs step S204 of the process of FIG. 12 and a
procedure that performs the process of step S304 of FIG. 13. The
stroke discrimination means 43 is configured by a procedure that
executes steps S401 to S403 and S406 of the timer 1 interrupt
process of FIG. 14 and a procedure that executes steps S503 to S512
of the timer 0 interrupt process of FIGS. 15 and 16, and the timer
1 setting means 44 is configured by a procedure that executes step
S305 of the rotation detection signal interrupt process of FIG. 13.
The ignition signal generation means 45 and the switch turn-ON
means 46 are configured by step S404 of the timer 1 interrupt
process of FIG. 14, and the timer 0 setting means 48 is configured
by step S405 of the process of FIG. 14. Further, the switch
turn-OFF means 49 is configured by steps S501 and S502 of the timer
0 interrupt process illustrated in FIGS. 15 and 16.
[0162] Although several embodiments of the present invention have
been described, the present invention is not limited to the above
embodiments, and it goes without saying that various modifications
are possible within the technical scope and spirit of the invention
set forth in the patent claims.
[0163] For example, although in each of the above embodiments an
outer-magnet type magneto generator provided with a magneto rotor
that is provided with a three-pole magnetic field at the outer
circumference of the flywheel attached to the crank shaft of the
engine is used, any magneto generator provided with a magneto rotor
that is rotationally driven by the engine and with a stator having
an armature core that is inputted with magnetic flux from the
magneto rotor and around which an ignition coil and an exciter coil
are wound would suffice for the magneto generator used in order to
carry out the ignition method according to the present invention,
and the magneto generator is not limited to being an outer-magnet
type magneto generator.
[0164] Further, any switch element capable of ON/OFF control would
suffice for the switch elements configuring the ignition switch and
the charging switch used in the ignition device according to the
present invention, and such switch elements are not limited to
being MOSFETs and bipolar transistors.
INDUSTRIAL APPLICABILITY
[0165] The ignition device according to the present invention is
able to be utilized as an ignition device for performing the
ignition of a variety of internal combustion engines. With the
present invention, spark discharges that rise quickly and moreover
have long durations can be produced in the ignition plug, enabling
ignition timings to be stabilized and ignition energy to be
increased, and enabling engine performance to be improved.
EXPLANATION OF NUMERALS AND CHARACTERS
[0166] 1 Magneto generator [0167] 2 Magneto rotor [0168] 201
Flywheel [0169] 202 Permanent magnet [0170] 2a, 2b Magnetic pole of
magneto rotor [0171] 3 Stator [0172] 3A Armature core [0173] 3a, 3b
Magnetic pole part of armature core [0174] 3B Coil unit [0175] 303
Primary bobbin [0176] 304 Secondary bobbin [0177] L.sub.1 Primary
coil [0178] L.sub.2 Secondary coil [0179] A Ungrounded output
terminal of secondary coil [0180] B Tap led out from secondary coil
[0181] C Grounded output terminal of secondary coil [0182] Lex
Exciter coil [0183] 4 Electronics unit [0184] 401 Circuit board
[0185] 4A Ignition circuit [0186] 4B Charging circuit [0187] 4C
Microcomputer [0188] 4D Power supply circuit [0189] 4E Rotation
detection circuit [0190] 4F Breakdown voltage detection circuit
[0191] C.sub.1 Ignition capacitor [0192] SWi Ignition switch [0193]
SWc Charging switch [0194] T.sub.1 Field-effect transistor [0195]
T.sub.2 Transistor [0196] S.sub.1 Thyristor [0197] D.sub.1 Damper
diode [0198] P Ignition plug
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